I feel this would be a good option for a turn, regardless of the variation. Opinions?

There is precedent in other games, certainly.

First you return your unwanted tiles, then everything's randomised, then you draw? So you could get a fair number of your unwanted tiles back later in the game.

I like the way the game works now. There's already a kind of elegant solution on this, as you can play any one tile on the board without it needing to be a word. So you have “throw exactly one tile on the board and get one random tile in exchange”.

For me the tile selection management is a large part of the game. Playing the full seven is a risky choice, and so is burning all your vowels. Getting rid of your nastier letters in a timely fashion without too much backslash is always important. This enriches the game with full another level of creativity and versatility. Not that this all would go away even if some tile change option was introduced.

I'm not sure if it would change much, on the top level, as skipping a turn in hopes (not even a guarantee) for a better set would be a risky endevour at best. Games are certainly lost on the bad tile selections and the early game does not matter that much on the big boards, so perhaps it would be an usable option.

It would probably be used in endgame parity play, when you'd pretty much know, what you'll get from the bag and at the same time could urge your opponent to draw the bag over the seven tiles mark… which might even cause a situation, where there are eight tiles in the bag, and both players just keep changing their tiles.

…yeah. Even if something like this was implemented, it would certainly take some thinking, and I don't see enough incentive.