a friend just bought a running/ driving 4 seater for 1000 but didnt notice when an adult sit in the rear his head is 2" above the head bar. i was thinking how to raise it, to cut it and raise it about 5-6 inches but putting like a 1.25 tubing inside the 1.5 tubing to help it keep its strenght. any better ideas or this work ok thanks

Nothing wrong with putting a sleeve inside the tube. This is a acceptable means of doing a splice. Drill a couple holes on each side of the splice for a plug weld to hold the sleeve in place. Crank the welder up a notch for good penetration and you will be fine.

I also used the sleeve method for extending a tube once. Where the two 1.5" pieces meet leave a 1/8" gap so when you weld the two pieces together it welds to the sleeve. If you were to butt the two pieces together at least chamfer the edges so you get good penetration, especially if you plan to grind the weld smooth.