Point about "disguising" words you think might be naughty. Don't do it.
The way the forum is set up, if someone types a word on the (short) list of banned words, the autocensor will catch it and post something else. In this way there is no danger of the member receiving any sort of sanction for breaking the forum's profanity rules. So long as the word is typed in clear with no attempt to circumvent the autocensor.
However, if someone changes the characters in a banned word so that the autocensor doesn't recognise it, and the word is recognisably the banned word when it appears, you will get an infraction for circumventing the autocensor. Thus, posting questionable words with funny characters is a bad idea.
I really don't think "shag" is on the banned list. There we go, it isn't. So don't be shy, if you want to use the word, be bold and upfront about it.