The YM2608 and YM2610 aren't all that different, actually.
But there is no pre-made tool to convert from YM2608 to YM2610.
In order to do the manual conversion in VGMs, you need to
- VGM header: set the YM2610 clock instead of the YM2608 clock
The value is the same, except that you need to add 0x8000 0000 in order to enable YM2610B mode. - data blocks: change the type of "YM2608 DELTA-T" data blocks to "YM2610 DELTA-T"
and add a ROM dumps of the YM2608 rhythm ROM as "YM2610 ADPCM ROM data" - VGM commands: change "YM2608 port x, write" to "YM2610 port x, write"
If there is any PCM involved (either ADPCM-A rhythm or Delta-T), you will need to fix the registers as well.
The register offsets of ADPCM-A and ADPCM-B (DeltaT) are different between 2608 and 2610. SSG and FM stuff is completely unchanged.
You'll need to look up the YM2608/2610 register maps in order to know what to change. - If the YM2608 song uses ADPCM-A rhythm, you'll need to add commands to set the start/end offsets of all ADPCM-A channels. (Those are hardwired on the YM2608.)
- If ADPCM-B/DeltaT is used, you may need to adjust the DeltaT start/end register values. IIRC the YM2610 has different offset multiplicators in order to support larger ROMs.