You should be able to copy the field that has the script trigger, then paste it elsewhere, specify a different field and it should retain the trigger setting.
Yes - that works - but I already have the fields set up and I just need to add the script trigger and wondering if there is a short cut.
In that case, I don't think so. It's up to you whether it is quicker and easier to replace the field instances you already have in place with the one that has the script trigger set, or to add the script trigger to the existing field instance.
One thing, though; you can apply the same script trigger setting to multiple fields on the same layout all at once.