Simon, Welcome. You were rudely treated without cause. Please give the benefit of the doubt to many very good posters here.
Your question is fair, in the following context:
The owner pilot may be permitted to replace one comm for another - in the tray. If there is zero wiring change, or work with tools behind the panel, a simple swap of one for another in the same tray is usually okay. You will find that there are "newer" comms, which are designed to slide into older trays. But, some homework will be required on your part with this, and your question does not provide enough information for anyone willing to help you here.
Sigtronics does make a battery powered plug in only intercom, and yes, you can install that too. But anything which involves a wiring change behind the panel will have to be accomplished by an avionics shop, unless the aircraft is non certified. BPF has summed it up nicely.
Welcome to general aviation - lots of really nice, helpful people, and a few others too....