Would a script be ok for Custom Formatting:
(as otherwise would be: rightclick cell, format cells, Number tab, custom)
i.e.: NOT able to use a formula, (NO Formula's)

Hi, looking for way to omit characters (numbers) in custom format where
examples might be: 1.5M 1.5B and/or 1.51BM 1.51B thanks.

to allow something like?: (not sure what correct version should be)
#,##0? ("?" for any alpha-character)
0?
#?