Is there a way to add Available Subs to an existing MP Save?

Hello! I've been hosting a 'serious' MP game for a few days now, and we're making good progress. Some of the regulars have suggested we should look into a slightly more capable ship soon. However, when I started the Campaign, I didn't expect to get as far as we've gotten. So I only added very few subs to the "Available For Purchase" list when I started things up. I'd like to add more, so we have more options when it comes to buying the next one. How would I go about adding new subs to that list for an existing savegame?

Thank you for any help!