I didn't write on my application after i printed it out. But, maybe someone here has and it must have not been a big deal. I would recommend putting that info into the application before printing it out. Once you have organized all the supporting documents, you can type all the info and then print it. I know it can be a pain in the behind retyping all that..but that's what i would do.
Also, I had similar issue as you...I ended my retyping my application at least 3-4 times if i remember...finally i was satisfied with it.
good luck