>Is there any way to modify ProDOS to read/write/format on 40 track drives?

If you have ProDOS 1.0.1 or 1.0.2, then i have patches for you.
First, make a copy of your orig. Disk. Then apply the following:

BLOAD FILER,A$2000,TSYS
CALL-151
79F4            should be 23; number of tracks
4244            should be 18; number of blocks (low order byte)
4246            should be 1; number of blocks (high order byte)
79F4:28
4244:40
3D0G
BSAVE FILER40,A$2000,L$6400,TSYS

UNLOCK PRODOS
BLOAD PRODOS,A$2000,TSYS
CALL-151
5209: D0 05 EA   for ProDOS 1.0.1
        or
5201: 18 EA EA   for ProDOS 1.0.2
BSAVE PRODOS,A$2000,l$2D00,TSYS
LOCK PRODOS

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And here is, what to do with ProDOS 1.2 and 1.3:

The patch according to Beneath Apple ProDOS is:
UNLOCK PRODOS
BLOAD PRODOS,TSYS,A$2000
CALL -151
58E3:40 (for versions 1.2 and 1.3, I don't know about later ones)
3D0G
BSAVE PRODOS,TSYS,A$2000
LOCK PRODOS

And to get FILER to format 40-track disks:
UNLOCK FILER
BLOAD FILER,TSYS,A$2000
CALL -151
426A:40 (for the 18 JUN 84 release, it's 4244:40 for the 1 JAN 84 release)
79F4:28 (for both versions)
3D0G
BSAVE FILER,TSYS,A$2000
LOCK FILER