Hi Henry, Yes you can change the tip, I am assuming the adaptor is one that will accept multiple ends.?? (Also I hope you just want to use it for something else, dont use a positive tip on a component that requires negative as its possible to blow a diode) If not the only way to do it is to snip off the part that goes into the ac/dc socket and reverse the wires...Normally you will have one plain wire and one with broken white line, to reverse the current configuration once you snip off the adaptor re connect the plain line to the one with the dash..and vice versa..If they are not marked put a dot on the one side below where you are going to snip and on the adaptor wire you have left, you can then see the way it is now and reverse it. I have drawn a rough illustration, I am thankful I play better than I draw, ha ha.
Fenderphil