My first job out of college was 2 miles from my house, so I rode my bike. At the interview I asked HR where I could put my bike, she says "we give you a parking space, you don't need to ride your bike". Had to figure out where the service elevator was and find an empty cubicle to park it in.
From experience biking to work in sweaty Florida... dry shampoo for your hair (it's like baby powder, they have brown and blonde versions), keep deodorant and baby wipes at your desk and give yourself a good wipe-down before work. Keep a change of clothes at work in case you get rained on.
Many coworkers changed outside of the bathroom stalls, by the sinks, out in the open at my last job. It depends on your personal comfort level. You could also try to track down an empty conference room / private office / storage closet to change in, or maybe look for the nursing mothers pumping room and see if it's open. Or if you have a restaurant/cafe next to your work like a Subway, pop into their ADA bathroom to change and buy a coffee for good manners, you might make a new friend with the morning crew :)
