I suggest a new pattern effect that toggles a hold mode on/off for all subsequent sample effects used, after seeing this being standard in furnace tracker and what a time saver it is.
For example, 0Hxy (01 = on, 00 = off).
This would make any sample effect persistent until it is changed, be it volume fades, portamento, note volumes or arpeggios. Shutting an A37 arpeggio off would be done with A00, or a volume fade with O00.
The toggle could be per effect column to avoid any nuisance when using more than one simultaneous effect.