I was toying with some different tunings and playing around with a slide that my friend had let me play around with, and I can understand how slide guitar can be like starting guitar all over again, and really learning a new branch of the music, but another friend walked in and told me that tuning the guitar out of standard would set me back to the start of learning, and it really didn't seem that way to me, it just seemed I would have to learn the new placement of notes and re-learn some chord shapes, but would playing in an alternate tuning really be like starting over? And am I right in assuming that slide guitar (like changing from rock to classical) would be like learning a whole new style if you're used to playing standardly?
New Tunings: Techniques remain the same, but you will have to relearn chord and scale fingerings. That could be harder than it sounds, as your fingers have likely developed some muscle memory. Don't let that discourage you, as alternate tunings can be a lot of fun.

Slide Guitar: Slide guitar is no harder than regular guitar, but it is incredibly frustrating for an experienced player to start learning slide and be a complete beginner again. The techniques with a slide can be considerably different, though slide is a lot of fun as well.
if you know how to make your way around the fretboard, new tunings she be a litte different, but you will pick it up quicker. if you memorized your fretboard your stupid, then new tunings WILL be hard.

Dont memorize everynote your fretboard, but rather know the shortcuts to jump around it. IE know where your fifths and octaves and 3rds are and what they are. Then the rest will be common sense.
If you dont find theory interesting, then DONT study it. IF your TRULY serious about playing guitar(enjoying), then EVENTUALLY you WILL WANT to study it.
Thanks both of you, I appreciate the answers. I'm just wondering, I didn't memorize the notes on the fretboard, I just know how to figure out where they are in relation to each other on the good, and that kind of gave me a memory of where a note is, if I use an alternate tuning and start getting used to the notes in that tuning, and their relations, will I lose that much ability with a standard tuning, or will I still be able to go back to that comfortably? Thanks .