Illarion.org

I suppose this would be a rather difficult one, as most likely a database change is required, but still i would like to throw it in:

Inscriptions that have a relation to time (like the moon runes in LotR, etc..)

So the inscription is only visible at night (which i guess would be least complicated) or in a certain month or single yearly date
or that might show a different text under the above conditions.

That is possible, and that with relatively small effort.

The question is for what? Do you have some specific usages in mind?