Novice LED questions
Now ever since the dawn of time, we have fitted an AC transformer in the panel which sends 24v AC and a 0v down to the handset which goes to the toggle switches and also the LEDS.


This is probably because when the system was designed at the dawn of time, 


They might have used 24 V incandescent lamps instead of LEDs.
A 24 V transformer was probably lower cost than a DC supply.



  I wish to ditch the AC transformer and fit a din mounted 5amp DC unit. My question is though, will I still have to fit the resistors? I know they should be needed to smooth out the current going to each LED but just wanted to check.


You will still need to fit the resistors. These limit the current through the LED so it doesn't blow up. You will probably need a different resistor value to get the same brightness from your lamps, when you switch from 24 V AC to some other DC voltage.

You can also buy LEDs or LED lamps with the resistors built in, which could save you having to assemble the resistors yourself.