I should have known that; many years ago, as a teenager in the late fifties -- I'm showing my age -- I was a Ham with call sign W2L** since appropriated by someone else, no doubt.
About getting the Text Substitution to work: I just went through this but haven't figured it all out yet. This is what I've worked out so far: You set up the substitution first in Sys Prefs, then from the app (I used TextEdit; it only works for certain Apple apps e.g., iChat, iPhoto, Mail, Safari and TextEdit) from Edit you select Show Substitutions, then check "Text Replacement" and "Replace All." Note, and this doesn't seem right, there must be spaces between the replaced figures for each new figure to be replaced with the substitution. I can't figure out "Replace in Selection." If I highlight a group of unslashed zeros, either with spaces between or none, nothing happens.
Since there are still a number of steps involved, seems like Automator would be the best way to go, if you can get that working.
Message was edited by: WZZZ