I had a similar issue where if the model was opened the mass properties parameters were not in sessions so various functions such as relations would not work. I did the following (because it was a mapkey being developed anyhow). Clicking Regenerate in the mapkey did nothing to update the parameters because Creo does not see anything as modified so it results in a message similar to the following, "Not Regenerated, nothing changed". I did the following to fix.
> Created a mapkey that opens the Model Player
> Checks off Regenerate Features
> Ticks back ONE feature in the model
> Clicks Finish...
This forces regeneration on the last feature and then parameters are forced to evaluate. This allowed my post regeneration relations to drive the parameters correctly.Ironically once the relations were updated a regeneration was required.