Use both English and western saddle?

  Would my horse have a problem

switching them out often.

I plan to use the English saddle the weekdays when I can't ride more than 2hrs

and western on weekends and longer trips
It shouldn't be a problem, just make sure both saddles fit well. I ride my horses English and Western, and there have been no problems whatsoever.
Yes, you can switch them out as much as you want as long as he isn't a green horse (he may get confused at first if so). If you are going to ride for several hours in a western, may be a good idea to get a seat cover for added padding and comfort :-)
As long as both saddles fit the horse properly, there is no problem riding both english and western. I did both HUS and WP with my last horse. Would even school him in both the same day with no issues.