Roof bars are easy.
From memory:-
To fit the roof rails, remove plastic strips running along either side of roof, and drill two 20mm holes in each at the point indicated by the fitting instructions, you will need new double sided tape to get them to stick back on.
While the strips are off, remove the blanking plugs bonded into the roof (30mm socket?), install new pillars using appropriate sealing compound - I used silicon sealant.
Refit strips, loosely attach rails, attach cross member, tighten up.
Then fit plastic cover pieces - if you don't silicon these in place they can disappear - car wash, wind etc.
So unless you fancy having two sets of the black plastic strips, rolls of double sided tape and fighting with silicon every time you want to swap, the answer is no they are not easy to swap on a regular basis.
