Transformation file based on dimension properties

dear BPC Gurus

I've created a transformation file which I'm using for importing transaction data from BW.

I'm trying to create a rule for dimension FLOW in the transformation file that:

If the G/L account type (dimension ACCOUNT, property ACCTYPE) is AST or LEQ, put FLOW as F99., i.e. *STR(F99)

If the G/L account type (dimension ACCOUNT, property ACCTYPE) is INC or EXP, put FLOW as F10., i.e. *STR(F10)

Is this achievable via Javascript?

I couldn't find any standard transformation formula that can do that....