Can I update add-ons, without updating GD core plugin?

I hired a dev team, to add some functionality to my GeoDirectory website. According to them, there was no way to add the functionality, without editing the core GeoDirectory plugin. So, if I update the core plugin, I lose all the customizations. Obviously, this is a major problem, as not updating plugins is just asking for security and/or compatibility issues to come up.

Until I can come up with a more permanent solution, I have no choice but to either:
A) refrain from updating the core plugin, or
B) every time there is a core plugin update, download the plugin, apply the edits, and then use the edited core plugin to update the plugin on my website

I see there are updates for every add-on I have installed.

I am wondering if it would be safe to update the add-ons, before I am able to update the core plugin. Or, would that break something?

Please advise.

Thank you.