From my limited knowledge (and asking Chatgpt) that is what happens. -Someone please correct me if I'm wrong- If I sell a credit spread to collect the premiums, then the volatility suddenly increases, the option I am short of should now be worth more. Now if I have to close the position early I'd have to buy it back at the now higher price hence the broker may ask for more margin as the price of the option ticks up.
Not necessarily. Reg t is based on moneyness and PM is based on shock value. Neither of which are explicitly linked to implied vol.
I agree with what others have said, that is, if the position has a finite risk, e.g., a vertical call spread, no naked short exposure, then the max loss cannot change. However, the max loss assumes that you hold the position to expiration. If you exit the position before expiration, it is possible that you could take a loss that is greater than the max loss. Prices may be out of whack. One or more legs of a spread may be overpriced or underpriced. Markets are generally efficient; that does not mean they are always efficient. Under such conditions, most traders would not choose to exit a position. But if you are forced to do so for some reason, you could have a loss that is greater than the max loss on a PnL chart. And the max loss does not account for certain external variables, such as dividends.