Really wise MOD, IMO.
As for the other point, yes you would need to have it installed in order to use it from within a MOD. However, I'm not sure at the moment if MODs with dependencies are being accepted into the MOD DB or not, hence the classification as a MOD Development Tool. But if you wanted to do it like the BBCode one, then yes you could put that requirement in the notes I guess.
What values can I use for the ID value?
The phpBB MOD Team have defined a range of values which are available for use by MOD authors who are only creating MODs for use on a single site, and you are able to use any value from within this range. Any new MODs which are submitted to the phpBB MOD DB after the start of November should not use any values in this reserved range, as the MOD Team are allocating reserved ranges to each MOD Author who requires them for MODs which will be released at phpBB.com. It is still possible, that older MODs you may have installed will use a value in this range, which you can check by looking in contants.php for any "define('PAGE_" lines, in which case you should not use that value.
Full details on this can be found here: http://www.phpbb.com/kb/article.php?article_id=149
If you plan to release your MOD in the phpBB MOD DB, then you will need to obtain a reserved value for your MOD, and will have to make the required changed to the relevant files, as the MOD Team will currently not validate and release any MODs which depend on having other MODs installed.
Can any member of the MOD-Team confirm this, please?
In short, does another MOD depending on Graham's PageID tool have any chance to be validated?
If so, suggestion: Add a reference to this MOD in the above mentioned KB article.