NEWELY entered cell value changes depending on the PREVIOUS cell value (VBA)

[Sleeplol]

Hi everyone,

I'm hoping to get a script that would change the value depending on what the previous value of the cell was.

Setup:
If user attempts to enter "VA, or BV, or PB" in a cell that has a value of "O" then the value becomes "VAx, or BVx, or PBx"

For instance if the user wants to select VA (vacation) over worked days but drag across cells over O (off days) then the O days become VAx instead of VA

Current:

Goal:

Thanks for any help with this