First off, it doesn't matter if you have a Mac. Everything would take place on your iDevice. Secondly, there aren't any MCPE mods for iOS. It's a lot more complicated to mod. If you want to mod you need an android device.
BUT, you can install maps. If you have an iDevice you need to jailbreak it. Currently, the newest jailbreak is for 8.4 but one for 8.4.1 and 9 will be around soon. If you are on 8.4, jailbreak then install Filza.
1. Download an MCPE map
2. Go into Filza and under documents you should find the map.
3. Copy the folder
4. Go into /var/mobile/containers/data/application
5. Look for one that says Minecraft PE
6. Then go into documents/com.mojang(or something like that) and then look for another folder called Minecraft worlds.
7. Paste the world in there
Also, there is xmodgames. You can find a link on the homepage.