Perform a period pressure

GROMACS version: 2019 or 2020
GROMACS modification: Yes

Dear developers or users:
I want to perform a NEMD by coupling period pressure (custom, like time dependent pressure), Some papers achieved this by modifing GROMACS code. Could someone kindly provide me a sample code or protocol. I learned C and python but I have no experience on such code modification and dont know how to start.