Swapping flat needles for circular

Is it easy to swap flat needles for circular ones when following a pattern for a Norwegian type sweater - any tips??

Are you planning on changing the pattern from knitting flat to in the round? That could be more complicated. If you’re just switching needle types it’s no big deal. You just start knitting with the circs.

Welcome!
It depends on the pattern. Many Scandinavian fair isle patterns are written for knitting in the round on circular needles. If you knit back and forth on straight needles (or circulars), you sometimes come to rows where the color that you want to use is at the other end of the needle.
What pattern are you thinking of? Can you give us a link or a name?

I would like to go from straight to circular to do away with the seam. This is a link to the pattern chart http://freevintageknitting.com/charts/vol103-no35chart.jpg. Could I start on circular needles then when necesary, knot back and forth on the same needles, or am I making it too difficult!!

I wonder if the methods for turning in these videos might be applicable.
Intarsia Knitting in the Round
Seamless Intarsia in the Round (I just love her voice!)

I sometimes find techniques for one particular demo useful elsewhere.

I think I recognize the chart from a favorit booklet. Sure, knitting on circulars up to the armholes and then changing to knitting back and forth on the same needles for the front or the back will work just fine. Check to make sure that you have enough sts after the ribbing to work the lice pattern continuously around the sweater.

Thank you so much for all your help, it’s been great and I feel much happier now about starting my project on circular needles.