A wastegate actuator will NOT cure boost creep issues. The issue is the hole for exhaust gasses to bypass the exhaust turbine is too small. It needs to be enlarged. S5's you can probably get away with just enlarging the holes, but S4's should have a larger flapper welded on and ported as necessary.

Taking the turbo apart is very easy. It's just turning box-end wrenches. I'd rate it about a 2/10.
I did my first one with a dremel and a carbide bit. Took a while, but got the job done.
If you snap off one of the bolts in the cast iron housing, it quickly elevates to an 8 on the PITA scale, though.

The stronger actuators BNR has are to help prevent the wastegate from being forced open by the higher exhaust gas volume associated with hybrid turbos. Adjustable rod lengths can also be used to increase spring pressure. But as RXSpeed16 mentioned, this is unrelated to boost creep problems.

I have a s4 motor and turbo setup and have a s5 hybrid to4b v trim (ported wastegate) on the way. Can I get away with mounting the turbo without adding a ems or upgraded injectors if I keep the boost at stock levels? Looking for a simple option to keep the levels stock for the time being. If there is no option I'll hang on to the turbo while i collect funds for a ems and injectors.

Those stock injectors will hold you back...There will be more air moving through the engine with that turbo, even at stock boost levels.

I suggest RTEK 1.8 and an upgraded fuel pump. That turbo is capable of over 300whp and really comes alive above 10psi.

Unfortunately rtek does not support my s4 jspec ecu, I'm hoping there's a temporary option while I prepare to get a haltech system.

You might be able to get away with larger secondary injectors and an S-AFC to trim the fuel. I wouldn't try it without a wideband though to be sure it's enough fuel.

Not sure if this would work but I'm thinking of using my US spec n/a harness and make the pin changes for a 13bt motor and extending the harness for RHD, then sourcing a US spec ECU, turbo maf and map sensor. If I go this route I can get a better tuning solution like rtek.

It would work. The trick is finding an N370 ecu for a decent price nowadays. For a little more money, digitaltuning can upgrade the N374 ecu's to the 2.1 version of their software. Now you have tuning capability and not have to modify your harness.