How are you deducing that the system is building abnormal pressure? The cap is semi vented and will vent under slight pressure but will hold to 16 psi under hot pressure.
When refilling your honda, you have to heat cycle the engine two or three times to make sure all air is expunged, it does it itself as the system cools down after warm up and sucks coolant back from the expansion tank.
Mind you, if you have a leak anywhere in the system, the system will not suck coolant back from the tank at all, so make sure everything is air tight, you may need to find a workshop that can do a pressure test on the system to see leaks. Moo ka presharr test wont work.
And if your system is not expunging air after refill then you have a high chance of damaging your engine. This is why workshops use a vacuum filer setup or a raised funnel setup to fill up the system and use various techniques to make sure all air is removed.
Sadly your 20w50 maarka ustaad mechanic owning 7 tools never knew that cars are a lot different from a 1950s british piece of crap on wheels.
