I want to keep my new guy as Lt, so I can play with any of my friends who come into the game. I almost have it, but I'm now at Lt 12, and all the missions/rewards are LC 2. Any suggestions?

this probably does not belong in feedback as a post (probably academy) but the answer is there is no way to stop yourself leveling short of not actually doing any missions at all. Even just shooting stuff will slowly rank you up (very slowly).

The best you can do is not spend any of your skillpoints which will keep you at your current rank but will still result in you increasing your current grade (i belive theres a brave few out there who are lt 50+).

So either make a new character and dont play them much except with your friends, or accept that your character will continue to gain levels.The missions are set for specific ranks, so your going to keep seeing them get harder as you go along since there designed for characters that are progressing in there ranks.

In the end it does not matter too much, if you really want to fly alongside friends who just joinned the game you can set them as squad leader and then match there level. Bringing out one of your old ships from that rank and having it pre-equipped with rank approperate gear will keep you about the same in space. I have the ToS connie set up like this for helping new players at lt.

I've heard of Ensign 51's

You can't stop your levelling, unless you stop playing. The next best thing to do is, when you enter a team with your friends, to pick one player as Squad Leader and use the option to match to the squad leaders level. This will increase (or reduce) your effective hit points and damage output. You can also choose to share quests (for example, for missions you already played but your team mate did not).

delete & remake the character

Create a second character....

Make a KDf toon. There are hardly any missions over there to assisst you with not leveling.

Ouch, just ouch...

Yup. I already did that. My other guy was a very dull Vice Admiral.

Unfortunately, this isn't possible... What STO needs is the ability to configure for a voluntary 'Level Cap' for characters. This would also allow character not to 'out-rank' the rewards for missions of his level, and allow Lt., Lt.Cmdr., and Cmdr characters with extra 'purchased' BO slots to max out the skills of the additional BOs before advancing to the next Rank...