Attiny10 with RSTDISBL and USBAsp
Given you are using this as an external programming circuit (rather than inline with your existing circuitry), I see no reason why it shouldn't work if you make the following changes:


Remove R3 - it is not helping you, and may well result in the MOSFET never turning off - this is because R2/R3 form a potential divider giving >0.5V at the gate when RST_OUT is low, which may not be enough margin to fully switch off a MOSFET of 0.7V Vgs(th). Current limiting is not needed for a tiny MOSFET like this.
Ensure the 12V supply GND is common with the programmer GND. Otherwise it won't work properly. There is no danger making a common ground like this (*).


Make sure that R1 is rated for 0.25W (or higher). It will dissipate about 0.15W when not programming.



(*) Assuming you are using a sensible power supply.