Sure you can edit the frequency tables. Low bytes of freq table start at 0x159c in RAM, and high bytes start at 0x1638 in my latest development version. The particular RAM location may vary a little between versions though, so if this doesn't seem to work, you can search for this string of bytes to find the lobyte table:
!byte $46,$4a,$4e,$53,$58,$5d,$62,$68,$6e,$75,$7c,$83
...and this string of bytes to find the hibyte table:
!byte $00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00
!byte $00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$01
!byte $01,$01,$01,$01,$01,$01,$01,$01,$01,$01,$01,$02
!byte $02,$02,$02,$02,$02,$02,$03,$03,$03,$03,$03,$04
!byte $04,$04,$04,$05,$05,$05,$06,$06,$06,$07,$07,$08
Actually, it is a little more intricate than that, since these tables are preceded by some other bytes that are used for frequency slide functions as well, so the real frequency table in defMON looks like this in the source code:
_player_notes_lo_slide:
!byte $00,$00,$01,$01,$02,$02,$04,$04,$08,$08,$0c,$0c ;To allow very slow slides too..
_player_notes_lo_finetune:
!byte $11,$12,$14,$15,$16,$17,$19,$1a,$1c,$1d,$1f,$21
!byte $23,$25,$27,$29,$2c,$2e,$31,$34,$37,$3b,$3e,$42
_player_notes_lo:
!byte $46,$4a,$4e,$53,$58,$5d,$62,$68,$6e,$75,$7c,$83
!byte $8b,$93,$9c,$a6,$af,$ba,$c5,$d1,$dd,$ea,$f8,$07
!byte $16,$27,$39,$4b,$5f,$74,$8a,$a1,$ba,$d4,$f0,$0e
!byte $2d,$4e,$71,$96,$be,$e7,$14,$42,$74,$a9,$e0,$1b
!byte $5a,$9c,$e2,$2d,$7b,$cf,$27,$85,$e8,$51,$c1,$37
!byte $b4,$38,$c4,$59,$f7,$9d,$4e,$0a,$d0,$a2,$81,$6d
!byte $67,$70,$89,$b2,$ed,$3b,$9c,$13,$a0,$45,$02,$da
!byte $ce,$e0,$11,$64,$da,$76,$39,$26,$40,$89,$04,$b4
!byte $9c,$c0,$23,$c8,$b4,$eb,$72,$4c,$80,$12,$08,$68
!byte $39,$80,$45,$90,$68,$d6,$e3,$99,$00,$24,$10,$ff
_player_notes_hi_slide:
!byte $00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00 ;To allow very slow slides too..
_player_notes_hi_finetune:
!byte $00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00
!byte $00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00
_player_notes_hi:
!byte $00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00
!byte $00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$01
!byte $01,$01,$01,$01,$01,$01,$01,$01,$01,$01,$01,$02
!byte $02,$02,$02,$02,$02,$02,$03,$03,$03,$03,$03,$04
!byte $04,$04,$04,$05,$05,$05,$06,$06,$06,$07,$07,$08
!byte $08,$09,$09,$0a,$0a,$0b,$0c,$0d,$0d,$0e,$0f,$10
!byte $11,$12,$13,$14,$15,$17,$18,$1a,$1b,$1d,$1f,$20
!byte $22,$24,$27,$29,$2b,$2e,$31,$34,$37,$3a,$3e,$41
!byte $45,$49,$4e,$52,$57,$5c,$62,$68,$6e,$75,$7c,$83
!byte $8b,$93,$9c,$a5,$af,$b9,$c4,$d0,$dd,$ea,$f8,$ff
Anyway, if editing the table seems to work in general on an NTSC machine I might add a specific NTSC version in the next release of defMON. I won't make promises as for when that might happen though.