By tripple tree, you presumably refer to a motorcycle type fork with three bars in the headtube area. These are really strong units, And I don't see any real Darwin award type issues. There really isn't any reason why the central tube couldn't be swapped out. The problems I see are that you would presumably need to get the axial tube in there with nicely fitted ends, then the crown races would need to be cut, and so forth. That doesn't strike me as dangerous, but it does sound like some neat work would need to be done. If you get really lucky the current axial tube is like a shim for the 1" tube, and you can just braze in or possibly epoxy in the races.
If the current tube is mechanical as TT normally are in the moto world, and you can remove it in total. then you could get some 1" 4130 and sleeve the ends with some tubing with a 1" ID, then braze than in place, turn it down, and you could braze on a race ring, Then true everything up with a lathe. It can be tough to do this kind of thing without reamers, and machine tools.
If you can't get the central tube out, it's a lot messier, and it would help to seel a part to give the right advice. If you have acres of room in there, even epoxy can work.
One issue you need to address before the above is whether the offset of the TT fork is correct for your Head tube angle and the trail figure you need. There are trail calculators all over the net, so that should help. The crown height also needs to be right.