I may be wrong, but 5005.5 is still QNI, so the 31 should be able to work exactly like your 18i when the Q-setter is used.
From the 18i parameter manual:
QNI The direct input of tool offset value measured B function and the
direct input of offset value measured B for 2-spindle lathe:
0 : Not automatically select the tool offset number
1 : Automatically selects a tool offset number
From the 31i parameter manual:
QNI With the tool length measurement function, a tool compensation
number is selected by:
0: Operation through the MDI panel by the operator (selection
based on cursor operation).
1: Signal input from the PMC.