I think, not much would happen.
The ECU would restrict the max RPM anyway (in this case, by lowering the pump voltage and hence the amount of fuel feed).
Suppose there would not be a set maximum (hypothetically speaking), you would perhaps have higher RPMs, but most of all, a destructive exhaust temperature, causing rear BB failure.
If your objective would be a higher RPM, I think you'd better tweak the software to do so
.
Perhaps injecting small amounts of water in the compressor (hence causing perhaps steam internally and higher thrust at same RPM), would serve your theoretical objective better.
Just my 2 c, and wild guess. I am not an engineer nor turbine expert, just some logical thinking.
Nicolas.