From me watching Pakistani analysts, the conclusion is what if there is a regime change in Iran as a result of this conflict, then it will be far worse for Pakistan then current regime is. Americans are not going to install a regime in Iran which won't serve the American interests and American interests are very much in an antagonistic way with the Chinese interests and America's local strategic partner India would welcome such new regime in Iran.
So lets set aside all the emotional, civilizational, religious and ethnic ties with Iran, to those Pakistanis have them and think in a cold, calculated way. I think, if possible, China should supply massive numbers of missiles to Iran which would be operated by Pakistani 'advisors' already with expertise in using those missiles. That's also a 'plausible deniability' scenario.