Many of the principles of game design rely on consistency - if a distinctive yellow-coloured barrel explodes when shot, players will expect this to be the same for all identical yellow-coloured barrels and will hopefully learn from it. Moments like this are especially important when the stakes are high - if a rule like this is broken later on in the game, exactly when the player needs it, they will be annoyed.

This extends to all sorts of implications when it comes to even basic level design issues. One stupidly niggling annoyance I have with TFC maps is difference in clipping techniques between them - some will have tiny ledges you can happily stand on, others will have similar ledges you can’t. As an avid pipebomb-jumper, finding out the ledge I was aiming for isn’t actually any use - and then falling to my death - is a minor irritation. Some single-player missions I’ve played have let you jump into certain areas quite happily, but jump into another identical one and you’re dead instantly without any warning or reason, simply because “you weren’t meant to be there.” Lots of maps change the definition of ‘railing’ to mean “you can jump over this, except when you most want to.”

As a player I expect the world to adhere to certain restrictions and for behaviour to be the same everywhere. If I can jump onto a metre-high wall in one level, I expect the same for a metre-high wall in the next. If this isn’t convenient for the map (maybe jumping onto the wall would let me get somewhere I shouldn’t), then an alternative solution should be found rather than stopping me jumping up entirely. This exact scenario happens a lot in ‘realistic’ shooters. In the worst cases, an explicit ability (“jumping over a fence”) changes completely each time you try it, without warning.

As a designer I expect the player to have formed a set of basic rules about the world: they know what they can do, how their character moves, the capabilities of their weapons, equipment and such. I want to exploit these abilities to give the player something to do, be it get past a puzzle or simply get from A to B alive. I won’t give them new abilities just for a few moments, or take something away from them without it being very obvious - I’d rather take a weapon away than a simple message saying “ooh, you can’t use that weapon here” and not letting them fire it. It doesn’t work.

Before you do anything, always consider the ‘rules’ of the game, and the expectations of the player. If you stop them doing the first thing they try to do - the same thing that has worked for them so many times before - and don’t give a reason, your design is fundamentally wrong.

So - for goodness sake - don’t do it!