would my foreign based IR carry across if I do the Instrument approach on the multi-engine commecial checkride
No, you foreign IR does not carry over to a US CPL certificate.
It's meant to do recreational IFR flying in the US.
You'll need to take the IFR written test an a check ride with a US examiner prior to undertaking the CPL training.
So you still need TSA for the IFR.