Switching between SSD boot drives

Hello - new to the forum (although I have been reading it for quite some time).

I built a new computer a year and a half ago and made the mistake of getting too small of an ssd for my main drive. I got a 128gb Samsung 840 Pro and then a 500gb WD Black HDD for the data. The build has been great, but I ultimately installed most of my programs (which are quite large) on the ssd which in turn has gotten pretty full. I only use the HDD for data. I do prefer it this way so that my work programs are on the ssd even though I know I could have installed them on the HDD. So I picked up a 256gb 850 Pro and want to switch over to it, but I want to do a clean install. I plan on unplugging all the other drives (including the 840 obviously) except the new 850 and loading up Win 7 clean. However, I see this as a lengthy project and want to take my time doing it.
So on to my question:
If I load Win 7 onto the 850 and then want to call it quits for the day, can I then shut down the system, unplug the 850, plug back in the 128gb 840 and have it boot back up like nothing happened? Then maybe next weekend I'll unplug the 840, plug in the 850, load a few programs, etc.. I really don't care how long the whole process takes. I just want to be able to go back and forth at will.
I'm trying to be able to go back and forth between the 2 boots until the 850 is where I want it and then I will just save the 840 in case of a failure or something.
But I don't want to get into dual boots or choices from the start-up screen. I just want it to see Windows on the 840 when that is plugged in and from the 850 when that is plugged in.
Is there any reason this shouldn't work?

Thanks in advance.

Set the new SSDD as first to boot in BIOS setup, then after install plug back in the old one(s) and trigger the other OS SSD using the one-time BIOS Boot menu key as Brian suggested.

This makes it convenient to go back and forth until the SSD is ready for prime time.

Tips here for getting and keeping a perfect Clean Reinstall Windows 7

Thanks for all the replies. I think I will ultimately keep them both plugged in once the new drive is all set up. So my new drive will obviously be C and I assume the old drive (which used to be C) will be assigned a new letter. Let's call it H for example. This brings up 2 questions:
1) If I later use the BIOS or the F11 boot menu to boot into the old drive, will the old drive then be seen as C and the new drive will become something else? I would assume it would.
2) If I have a program such as Acrobat Pro on the original drive (now "H"), can I launch and run it off that drive even if I have booted into the new drive? Or do I need to reinstall it because it needs to see the new C drive registry? I know I'll be able to eventually see this via trial and error, but I'm curious if I will have to reinstall everything or if some programs can stay on the old drive.

And if I have the time and the patience to do it, is this still a better option than cloning? I have a copy of Acronis True Image, but I guess I always thought a clean install was best.

1) If I later use the BIOS or the F11 boot menu to boot into the old drive, will the old drive then be seen as C and the new drive will become something else? I would assume it would.

When you boot either OS, that OS (disk/partition) should been seen as the "C" drive.
If that is not what you see, let us know.
It'd be best if you post a screen print of your disk management.
Here is a tutorial by Golden:
Disk Management - Post a Screen Capture Image

I have multi-boot PCs, and I remove the drive letter for other (not booted) OS drives/partitions.
That helps keep me from making a mistake and making a change to the wrong (not booted) partition.

If I want to see or access other "OS partitions", I temporarily do one of these:
- Assign a drive letter
- Mount a System Backup Image

2) If I have a program such as Acrobat Pro on the original drive (now "H"), can I launch and run it off that drive even if I have booted into the new drive? Or do I need to reinstall it because it needs to see the new C drive registry? I know I'll be able to eventually see this via trial and error, but I'm curious if I will have to reinstall everything or if some programs can stay on the old drive.

No, you can't run an installed program that is installed on the other OS.
Installed programs need to be installed on each OS where you want to run them from.

Some programs have Portable/Standalone versions, so you can have a single "copy" of that program and use it from either OS.
I don't have Acrobat Pro, but I would GUESS that doesn't have a portable version.
You need to look at each program you use, and see if a portable version is available.

Thanks again for the replies. I figured I would have to reinstall the programs, which is no big deal since I'm taking my time on it.

So tell me if this scenario should work:
1) I install Win 7 on the new ssd after unplugging everything else.
2) Once I have windows up and running, chipset drivers, lan drivers, etc., I plan on plugging in my mechanical drives (internal data drive, internal backup drive and an external backup drive) so that the new OS sees them.
3) Then I'll probably plug in the old ssd and use the BIOS to make sure it boots to the new one.
4) Now I should be able to copy any files I have on the old ssd over to the new one since it will be simply seen as an additional drive (even though it has an OS on it).

Sound right?

And once I set the boot priority in the BIOS, I shouldn't have to choose anything off the start-up splash screen. Correct?

Some of the programs I use keep all my customization files on the OS drive deep under AppData. I tried moving them and the programs protest (many of these are Autodesk programs and they are not very flexible. Low flexibility, High Price - I believe that is their logo) so I may want the ease of grabbing something here or there. I have them on 2 backup drives, but I may want a visual check to make sure everything is the same once they are up and running.