vgmrips

Well... In theory you can change banks by changing the "PatchFile" entry to make it point to another bank.

Unfortunately the format is just a raw dump of the instrument data from SB16.VXD and I don't think that there is any editor that reads/writes that format directly.
So in practise, you will not be able to use your own instrument banks.

Short description of the bank format:
- 128 melodic instruments, followed by 128 drum sounds
- each instrument has 28 bytes
- The instruments consists of values for the OPL registers: 20h 40h 60h 80h 0E0h 23h 43h 63h 83h 0E3h (0Ah bytes total), then 0Eh bytes are ignored, then there is register 0C0h, the remaining 3 bytes are ignored as well