Just had a quick view at bootmgr version 6.2.9200 and noticed there where some difference to 6.2.8250, which mean it did not recompile well in modified condition. Since time is precious these days, I put up this information just in case, for future reference. It's basically just a bunch of notes found, that I made last time I successfully did this on version 6.2.8250:
8250 disable bootmgr digital signature:
0f8862020000 -> 909090909090 (6 nops)
8250 self signed winload without testsigning;
7415 -> eb15 (unconditional jump)
7507 -> eb07 (unconditional jump)
That's a stripped down version of the notes, as the rest makes no sense at all except to myself.