Should China relocate their H-6 bombers in Pakistan, in preparation for the bombing of US assets used in the invasion of Iran?
Only if there are signs of a ground war. It'd take months of preparations so there won't be any surprise.
I hope you guys are joking or this is delusional of the highest level. China will never ever join militarily in a war with US for Iran. The most China will ever do is provide them with weapons and ISR. Infact, China's satellite ISR will be the most important support that Iran can get and will most certainly have huge impact on the battle outcome. In terms of weapons also, China will not provide anything that can be visibly point at China. So, no Chinese weapon system.
For Iran? Of course not, or else China would be helping more now. Also, if China was providing ISR to the Houthi, what makes you think China isn't already doing it for Iran?
Many things need to happen for it to happen. First a ground invasion by the US, which I think is unlikely. Trump has no appetite for a ground invasion, he'll most likely just bomb the nuclear facilities and declare victory. However, China should be prepared for this possibility. Second, Iran needs to show a will to fight, China can't be entering a war to support a South Vietnam. Third, Iran needs to swallow its pride and realize that they need a backer. They can have China's respect, but it will not be an equal relationship. After the war they will need to go all in on Chinese weapons systems and give access to China ports and airports to operate from.
For China the importance of this is that it's the most realistic port China can get in the ME, and completes the string of pearls from the SCS to the ME and Africa, thus ensuring China's energy security and weakening the US's trump card in the event of a direct conflict.