I'm not saying ever, I'm just saying the Bears shouldn't make a mid-season swap. If J'Marcus Webb was playing 'Gate 68' bad, then it'd be a different story, but Webb isn't physically over matched at left tackle. The majority of his mistakes can be corrected with better technique and through experience. Putting Gabe Carimi at left tackle now would do more harm than good. Unless you're getting reps at both sides of the line as a backup swing tackle, it's just too uncomfortable of a move to make on the fly. I'm not saying it can't be done, I'm just saying it's not ideal.
I agree with Sam about keeping the offensive line as it is for the next game. Part of that is because I think it's better to give Carimi an extra week off for his knee, and part of that is because having his first game back after a long layoff to be in Philly would be a tough go for the rookie. Give him an extra week, then if he's 100% and ready to start they can let him have his first game back be a home game.
Coming out of Wisconsin, most scouts tabbed Carimi as an NFL right tackle or even a guard. I think the evaluations of him kicking in to play guard was more along the lines of scouts just covering their bases if a team were to go that route. He has tackle size and tackle feet, and unless you have two real good tackles in place already, a move inside to guard would never happen. Now for the record, I think he could play left tackle in the NFL. And in my opinion, the Bears having Carimi play RT with Webb moving to LT was the wrong move to make. Maybe with a full off season of OTA's they'd have had more time to evaluate the two, but that's what they decided and they have to live with it for at least the remainder of this season. For the sake of continuity and for allowing the line to gel you want to make as few moves as possible with the starting 5.
I'll argue that the offensive line is the position that's most important to have continuity in. You have to get a feel for what the guy next to you is doing. Double teaming a d-lineman, then releasing off to pick up a 2nd level defender takes time to master. It takes time to have confidence in the guy next to you to know when it's ok to release. It's not like you have time to ask the player next to you; "Do you have full control of this guy, as I'm about to release him to your control and peel off for this scraping linebacker." It's all about feel. It takes time to know how far inside a defender can slant before you have to help out. Passing off a stunting d-lineman while knowing when to look for the looping defender is something that you just get a feel for.
Flipping sides at tackle is a tough move mid season, again I'm sure you can find instances where it worked, but it's just not ideal. Even though Carimi played the left side in college, the NFL is a new set of challenges. The last few months he's gotten accustomed to the right side, a move back to the left would require some getting used to. The stance is different, the kick step angles are different, the hand placement is different, the pass protection help you have to be prepared for comes differently, the assignments are different, the line calls are different, and getting used to Chris Williams on the right would be an adjustment too. Gabe Carimi may be the exception that can step in and seamlessly do it, but with the Bears still in the playoff hunt, I don't think they'll want to take a chance.