BG44K won't fix the injector, they need removing, flow testing and proper cleaning, if they can be salvaged at all. If its bad enough to cause a persist ant misfire then get them done sooner rather than later
Your standard injectors are fine for a TTE420 - only need a FPRV to up the fuel pressure as the 136Bar item you have now won't be enough, and no you cannot run different injectors without a suitable map, which you won't get from APR