Yes, it is possible, but it is easier to load several transient profiles (link with an example: https://www.afs.enea.it/project/neptunius/docs/fluent/html/ug/node225.htm)
It should be possbile, but it is very difficult to implement as a single UDF.
I think it is better to:
1) Define a Single transient profile for Each velocity inlet
2) Load these UDF separately through FLUENT UDF compiler
3) When specifying Your inlet boundary conditions, the velocity value is no longer a number, but the EXACT UDF you have defined for that given inlet (select the exact UDF from "user-defined" option)
In this way, Your problem is very easy to be implemented.