What are consequences for minor content changes?

What should I be careful not to do?

[300m]

I have about 20 pages that I need to make minor content changes on. Its going to cover the same thing that it already does, but i need to update it soon and before I take that step, what should I be aware of before hand?

These 20 or so pages are ranked pretty good and i have put a lot of work in to getting those rankings. I would say 80% of them are ranked #1 and the reamaing fall between #3 and #4.

I really dread having to make these changes because it took me a long time to get them stable in the serps and if the risk of losing the rankings is drastic, I may end up not doing it.

What i want to do is simply keep 90% of the orginal content that is on these pages, but add not more than 100 words per page(they are feature updates)

Would i be better off not doing them all at the same time? Should i do 2 a day over a month? 1 a day?

After the past year of 301's issues, supplemental issues, rank/tank scenarios I would hate to have to go through any of that agian. I have had stable rankings for 6 months now and want to keep it that way.

Does anyone have any suggestions for the safest way to acomplish this goal without suffering?