My understanding is that you cannot modify the main game. If you could do some of the things you suggest, you might as well scrap the leaderboards.

You DO have access to everything that was used to make all those missions. I think 4 of the mission scripts can be looked at. I'm sure that's not what you really want to hear; but I suppose its possible that one day the developers will release the missions and allow you to change whatever you like. I guess they'd turn off the leaderboards though.
You can make your own weapons, but you need to then create a scenario in which you can play with it.

Once you've unlocked the Strike Suit (i.e. completed Mission 3), I'm pretty sure you can then choose it for any mission you like, providing you have finished the level in the assigned ship at least once.

Two pieces of advice, given the types of questions you've asked seem to suggest that you want to make the game easier in places: (apologies if I have mis-read your situation!)

1. Replay earlier missions with the strike suit e.g. even level 1, both to improve your skills but also to get unlocks which definitely help.
2. Practice using "flux" as efficiently as possible - e.g. fire only the right number of missiles at a fighter craft to destroy it, no more. You'll gain almost as much flux as you spent.

I hope that helps!

Thanks for this detailed response. I'm a little star struck to hear from a bona fide developer. I have a big programming / game design hobby, so you're basically a celebrity! You've confirmed my suspicions about the nature of the mod tools, for which I'm very greatful.

Two cents from a big fan: Wanting these features was born of a desire for developer access. The mod tools appear very empowering, but my personal interest tends to be changing rules and altering vanilla content. Once I thoroughly experience what a game has to offer, I want to experiement with it!

I imagine that for every tinkering code-monkey like me, there are ten folks who'd rather know their leaderboard rank - I'm just sad to find dev consoles obfuscated and the "cheat code" era behind me. ;)

But I digress. I'm in love with these games, so please keep 'em coming so I can throw money at you by the fistfull.

Kind Regards,