Secondary fuel pump coming on under boost

My car has a secondary fuel pump that is set to kick on at and above 1 psi with a secondary trigger needing to be above 70% tps. After watching this module is it correct to say that it will be very hard to tune when my fuel pressure rapidly changes when the second fuel pump kicks on. Also would that be something that you could possibly make a fuel modifier table for

It's the regulator, rather than fuel pump, that sets the fuel pressure - provided the pump has sufficient flow to exceed the demand and actually have an excess to be bled off and returned to the tank.

If the regulator and/or return plumbing doesn't have sufficient flow capacity, and isn't able to bleed off the excess fuel supply the pressure will increase.

As you're setting up the secondary pump to operate only when there is already a significant amount of fuel being bled off by the injectors, you may not need to uprate the regulator and/or return lines.

Because of the way regulators work, there may be a small to negligible pressure variation in use, but this may be factored into the normal tuning process - you may just need to try running the vehicle and monitoring if there is a problem. An accumulator will help dampen any pressure spikes that may occur with the pump's switching on and off, if it is a concern.