Another option is to maintain extra property:
MATERIAL_DI50 - PERCM - containing member id of corresponding %FAM%.INP
The you can use:
*LOOKUP SameCube
*DIM PERC:MATERIAL_DI50=MATERIAL_DI50.PERCM
*DIM CUST_PREV_DI50=CUST_PREV_DI50.GROUPE_DE_CLIENT
*DIM TIME_DI50="%Y_%.12"
*DIM ACCOUNT="ACC_62"
*DIM PHASE="C_101"
*ENDLOOKUP
Select all required base members and
*WHEN ...
*IS *
*REC(EXPRESSION=%VALUE%*(1+LOOKUP(PERC)), PHASE=%PHASE_SET%)
*ENDWHEN
Without FOR/NEXT but extra property to maintain.
Vadim