Keith;

If the coil is warm, even very warm, but still works as it should, not to worry. Ignition coils are just that...a coil of wire...actually two (primary and secondary), and they will generate a certain amount of heat during use when power is applied and interrupted continuously to generate spark.

If however you turn your IGN ON for some reason, and leave it ON without running the motor for a while (to do underhood servicing or some such thing), and the points happen to be closed, the primary coil will have a continuous 12V applied and I expect will get pretty toasty. There's nothing wrong with turning IGN ON and doing servicing with motor not running, but for the sake of your coil, avoid doing this for an extended time.

Cheers