I like the idea of a checksum, as it will be unique, I wonder what tool windows users will 
have to do this with or could 1 be shipped with LMMS?

anyway heres an example of using sha1sum on linux:-

mikobuntu@mikobuntu-Aspire-5332:~$ echo | sha1sum ~/vst/argotlunar.dll 
c4890a187c8367e6106c5e46967a0d8eb919672e  /home/mikobuntu/vst/argotlunar.dll

hth Mikobuntu

> BTW I was looking that in project files, there is usually absolute path
> stored for sf2 or samples, if they are opened from custom locations.
> Maybe those could use ame xml configuration file, if this will be working
> well for VSTs ? In that case I think there could be some hash or checksum
> instead of plain file size .
> Best regards
> -Mike