I'm glad Sue stepped up and answered. I hesitated because I was wondering about the different gages between rib and seed.:think:
I expect you will find the rib will draw together to reduce the width of the scarf whereas the seed stitch will not. This may not matter to you or for a scarf.
If it does matter, you might want to use a size or two larger needle for the rib, then switch to a smaller size for the seed stitch.
Sue, do you think that would help or might decreases be needed between rib and seed and then increases when switching from seed back to rib?
Or I might just be over thinking it.:shrug: