With movies sometimes a larger file with the same name is not really the same... and with MP3s the feature you are requesting will almost always result in corruption...

\•/Disclaimer\•/
This is untested.
If it doens't work
Don't complain.
/¯\Disclaimer/¯\

If you want to trick XoloX into resuming , try adding the following to your resumeinfo.txt:


------------
JOB
# <- A job # that isn't in use.
1
blah blah blah <- Search query to find the file, eg: "matrix divx" (no quotes)
x:\path\xolox\downloads\filename.ext <- use exact file name to download
######### <- new (larger) file size
2
00000000 <- CRC (dissabled, so it's 0's)
# <- # of failed segments (set to 0, unless you like seeing a number there)
NONSAVE <- If other downloads have something else here, use that instead.
SEGMENT <- start segment info
1 <- segment 1
x:\Path\XoloX\temp\JOB-Segment#-1.xlx <- # = job number
0 <- denotes start of file
38731181 <- length of already downloaded segment (in bytes) minus 2048
------------

Then just copy/move your partial file to x:\path\XoloX\Temp\JOB-Segment#-1.xlx and start XoloX.