Not true. Heating a bat is considered altering it, but once it cools back down to relative ambient air temperature, it's no longer considered altered. The ASA definition of an altered bat is "When the physical structure of a legal softball bat has been changed." It does not say "When the physical structure of a legal softball bat has been permanently changed."
ALTERED BAT: When the physical structure of a legal softball bat
has been changed.
That phrase is all encompasing of the past tense. To allow for the cooling of the bats in this scenario, the rule would have to say the physical structure is in a changed state.
There is no rule to support such action. That's up to the League or Tourney Director to decide, not the umpire. The umpire can only eject a player for having an altered bat in the batter's box.
B. When a batter enters the batter’s box with or is discovered
using an altered or non-approved bat.
EFFECT: The batter shall be ejected from the game, and if in a tournament, shall be ejected for the remainder of the tournament.
My bad, I read the rule slightly differently when I first read it. I thought it said
having used.
Notice the language difference (has been vs. using) ... one is past tense, one is present tense? I humbly suggest that if you are relying on the tense of Rule 7 to say that the batter can only be ejected during his at-bat, then you can't ignore tense in Rule 1 to say a bat can be de-altered.
All that being said, I will modify my previous positon to say that no one is ejected but none of the heated bats can be used.
Now here's a question ... can you take your at bats without a bat? Meaning, if we have no bats to use can we step in the box and have the pitcher pitch hoping that we get walked more than we strike out?