Can you assemble a fly fishing rod outfit by using components from different manufacturers?

Question
In a couple of places I've read something to the effect of having a "properly balanced rod" and using leaders and fly line from the same manufacturer because they will have the right amount of bend (flexibility) and will transfer energy better while casting. I do understand that for a 6 weight rod I should use a 6 weight line, but can I use a fly line from say Orvis, on a rod made by Sage using a reel made by XYZ? Along the same lines, I know that some stuff in fly fishing has been standardized. Can one use spools from a different manufacturer on a reel from another?
Answer
reel spools are not interchangable with different models and makers,because of design differences.There are some components of fly fishing that can be used in mixed company,lines by other than the one it was created for,and leaders and tippets and stuff,also the components of the rod itself can be used in some situations to create a custom job,just like automobiles they can be modified to fit the individual's needs and substituted where that is ok,it might not be pretty as a picture,but if the creator is skilled in his craft,it can be a beautiful thing to use.the standards in fly fishing are so someone in New Zealand can tie the same fly as one in Ireland and have it represent the same creature it's mimicing.A blue dun is the same fly pattern worldwide,wherever it was tied.Some local variations are common,because of the availability in materials.I have a vintage fenwick fly rod with scientific anglers line on a pfleuger reel and it works fine.There's a black wooly bugger on the tapered leader at the buisness end.