How to change openstreetmap-tiles-update-expire to use Geofabrik updates

There are probably a couple of different reasons why you might want to apply updates from Geofabrik's Egypt updates rather than the whole planet - one is to minimise the size of the database as it grows, the other is to minimise the amount of data fetched from a remote server.

It's perhaps worth mentioning that if database size is the main concern, you don't need to worry since openstreetmap-tiles-update-expire trims the update being applied to just the boundaries you're interested in (you'll need to edit that line to match the latitude and longitude of Egypt).

Assuming you really do want to use Geofabrik's Egypt updates you'll need to edit the "baseurl" line in /var/lib/mod_tile/.osmosis/configuration.txt . That will normally look like this:

baseUrl=https://planet.openstreetmap.org/replication/minute

and that file is created like that by this line in the script, which calls "osmosis". You can either change osmosis to create the default differently (have a look at the parameters that osmosis supports, maybe there's an easy way of doing it) or manually change it - there's actually a line in the script that does just that in order to change the URL to use https (which is now required at osm.org), so you could modify it to use your desired location.

You'd then want to remove the trim_osc code as you no longer need to call it, and only call the resulting script once a day because that's the frequency of updates. You may also want to increase "maxinterval" in configuration.txt because you want to apply more than an hour's worth of changes at a time.

I haven't actually tested any of this, so I've left this answer editable to you can add in any missing steps.