i am not sure i understand well. Do you mean that you want the tool to use more realistic switching activity - in which case you should read an activity file (.tcf, .vcd, .saif)
Or is your point to have it propagate from top level once you set some values there.
In RTL Compiler there is quite some flexibility on this aspect. you should check some attrbutes as below and see which suits best - i can suggest which would work , but i think i did not get your question well.
lp_default_toggle_rate
lp_asserted_toggle_rate
lp_computed_toggle_rate
Same above you will find for probability as well.