American television sets are designed to work with the NTSC colour system, Ireland uses the European PAL system. The tuners are designed to find a different set of broadcast frequencies so you will not be able to pick up "off air" broadcasts. It will not be possible to adapt the tuner.
The US standard definition scanning system uses 525 horizontal lines, the European system is 625 lines. US pictures are scanned at 60 frames/second, European uses 50 frames/second. US mains is 110 volts/60 Hz, European is 230 volts 50 Hz.
You can overcome the mains voltage difference by buying a thing called an "auto transformer", which will cost about £20. But the different line scanning system will lead to distorted pictures.
Most television sets made by mainstream manufacturers (Sony, Philips, Panasonic etc) sold in the European Union are capable of showing American standard pictures if they're fed in through a SCART socket. But it is not likely that American sets will handle PAL standard pictures.
Most television accessories like DVD players and Freeview boxes are connected by SCART lead, there is no guarantee that all American televisions will be fitted with SCART sockets. (SCART is a connector standard developed in France and adopted throughout the EU).
If something goes wrong with the television you will probably find getting support or repairs will be very expensive, difficult or impossible.
If you are importing a television set from the USA then you will almost certainly have to pay import duty before it can be released to you by the courier. Make sure that you know how much that will be and add it to the price.
The choice is yours to make, but you must consider all the factors involved in owning a television set, not just the up-front price.