There is no option, but if you can type a resume point, then use a bit of code to check the incoming file in a CTCP event. Then code the rest there. I've not seen the option to resume from a set byte in the file, so I can't tell you how to do that. Last I checked (many versions ago) mIRC did NOT roll back files.
It's also possible that it's doing a CRC on the last few bytes vs the next few bytes to ensure it IS the same file. I might do some testing on this, but not right now...
