It probably wouldn't go for that long. But good point though.

It's not wishy-washy. I, and others, have put a great deal of time and thought to this and I have stood firm on this option from the beginning. If and when my players desire to lower certain characteristics for whatever reason, this has been, and will be, the ruling.

Not to sound blunt; but why ?

The only reason I can think of for permitting (and not simply refusing) the request to trade back Characteristics for XP, yet permitting it at only a "half credit" rate, is the worry that the practice will be abused. In turn, by making the rate of return on the trade so poor you eliminate any meaningful chance of its being abused.

But as I said, abuse is more effectively policed by simply overseeing the character creation process. If you're worried about abuse, only allow people to do this when you agree with what they're doing and simply veto any "abusive" practices. Or, more simply, just ban the whole idea outright if you don't trust your players to use it properly. After all, it's not even permitted under the official rules anyway.

If you have a different reason for your thinking other than guarding against abuse, I'm interested in hearing it. But I can't come up with one.

Also, why " half "? Why not "three-quarters"? Why not "two-fifths rounded down"? Where does the 50% exchange rate, specifically, come from?

If you are decreasing for a certain amount of time (like to display a kid) wouldn't it be appropriate to hold back the additional exp they would have gained for the lowered stats, until they "grow up". Last I checked even though a kid thinks they know as much an adult, they do not. If you held it back until then, it would be a mechanical way to show growing up maybe?

If for instance you were doing a 3 part campaign like the prequels, or he'd be grown for at least the second half I could see doing that.

Side note:

I did that in a campaign a few years back (it was a GURPS fantasy game). The Player was a new add in the fourth session. She wanted to play the young apprentice/daughter of another player. I knew I'd be doing a few 2-3 year time jumps in the campaign, and after looking at her character I mentioned just lowering her stats "for free" instead of buying them down (GURPS intrinsically allows this). My reasoning? Buying them back up when the character "grew up" using EXP would cost twice what she gained for lowering them.

She agreed, we dropped a few of her stats and after the first few time skips just bumped up to "starting values" for free. In the long run it saved her some precious EXPs, but she started with a few less "cool things".