My old serger didn't even have rolled edge capability, so I've never done it. In my book it says to use one needle, and to use it for very lightweight fabrics, such as silks, crepe de chine, etc. I want to use it to hem flannel receiving blankets, will I need to alter the settings at all?

It may depend on the machine, but mine wouldn't need a different setting to do different fabrics. The only difference is that you might want to increase stitches, since heavier weighted fabrics don't want to roll up as well and you get little pokey things that stick out. Maybe a 3 thread flatlock would work nicely? That sort of gives the edge a satin stitch kind of look.

Oh, I just love rolled hemming! It's so fast - it's my new favorite for anything I can get away with using it on, including the raw edge of ruffles on the bottom of Amelia's pants and skirts with a flounce for me, on a lighterweight fabric. I always follow my serger's instruction manual (one of the few times I ever looked at it), which says to remove the left needle.

Using a heavier fabric, I would just practice a bit on scraps first. I'm not always consistent in how far away I guide the raw edge of the fabric in relation to the needle & loopers and everything. This can be a big problem if you're asking your serger to roll too much fabric, if you have the raw edge too far to the right - does that make any sense?

And you might consider using wooly nylon in the upper looper. Even though you're not using knits, it will fill in the space between the stitches.

I don't disengage the serger knife so it doesn't matter if you are a bit too far to the right.
My serger requires I remove the "stitch finger", the left needle, and there is a switch to put on "R". Play w/ your tensions on scraps and see what works best. Once you get it going it is really easy. :)