You are the BSS? What do you mean? You are developing a BSC software?
As we already said, the value send in the PC command indicates the absolute power.
it’s not possible to send information that means + “x” dB or – “x” dB.
So yes, you should send the absolute value of the power in the sacch message, and ensure this value is never less than the MIN MS TX POWER.
The MS will just follow the command from the BTS, no improvisation 🙂