I'm adding one word on my title tag and switching some words around - do you think I'll get slapped in the SERPs? This will be on my index page.

Try it! You can always change it back.

I change often my titles. No problem if you don't make spam in title. I ranked in relevant positions just after change titles...

If this makes things better for your sites visitors, then yes go right ahead!

Well, it won't be a problem,and we often do that, but don't make it so spam like!

You'll surely experience a sudden change or drop in your ranking if you change your title tag. But you'll regain your position after a while. In the meantime, you need to build quality links using a new anchor text that matches your title tag.

Yes, as above just make the changes.

SEO is best viewed as empirical as there are so many variables involved it's impossible to know for sure... give it a go and let us know how you got on.

I don't believe small changes will cause a problem but we did hit a temporary (four month) penalty when we significantly changed our website and title keywords (website design town a changed to website design town b).

CHANGE is GOOD! I often go through and update my titles/meta every couple of months. Google likes to see change and fresh unique content!

I made a small change a few months back and it did not negatively affect our serp rankings.

Well, it really depends if you ruin the sequence in your keyword your trying to rank on the SE. But if it doesn't then there is nothing to worry about it.
But I think your SERP will change depending on your current backlinks. Since updating your page will send the Google bot back to your site for Cache update.