Yes Oz, any player or substitute may attempt the throws under NFHS rules.
Rule 8-3: The free throws awarded because of a technical foul may be attemmpted by any player of the offended team, including an eligible substitute or designated starter. The coach or captain shall designate the free thrower(s).
Note the plural in the last sentence. In fact I had a sitch about a month ago where a player got a "T" the coach came unglued, he got a "T", so he started using profanity, he got another "T" and was ejected. Now team B gets to shoot 6 throws and could be attempted by 6 different players.
I would be interested in your list of differences between FEEBLE
and NFHS/NCAA rules.
Mike