The TPMS light comes on at 75% of the initialized pressure. For example, if you initialized the TPMS at 46psi the TPMS dash light will come on at 35psi.
As far as I can determine, since FMVSS (Federal Motor Vehicle Safety Standards) are involved, there is no way to change this percentage.
However, if (following our example) you run your tires at 46psi and instead of having the dash light come on at the prescribed 35psi, you want it to come on at 30psi, then all you have to do is TEMPORARILY adjust your tire pressures to 40psi and re-initialize the TPMS. After initialization at 40psi, re-inflate all your tires to 46psi - the TPMS light will now come on at 30psi instead of 35psi.
Certainly not as elegant as being able to adjust the percentage, but still not an onerous workaround.
HTH