Rest API parameters not initialized soon enough

Here's the senerio I am calling TeamCity via the rest api

I set a property called TAG_NUMBER via the api

I notice that TAG_NUMBER is not set until after the VCS section has run.

I have a vcs rule that uses tag number that does not work do to this

+:%system.TAG_NUMBER%=>.

if I pre set system.TAG_NUMBER to a value (that is supposed to be overridden by REST) it will use that value.

Once the build steps are started system.TAG_NUMBER gets the value it was passed.

Please help.

Also Is there a way to pass parameters between builds (ie the finish build trigger)

Thanks