When job postings give you specific instructions, they really mean it. So, for instance, if my job posting requests a "one-page cover letter," what I want from you is a one-page cover letter.
So it's a bad idea to send me this:
"I apologize in advance. I simply could not reduce the length of my cover letter to one page."
Really, you simply could not? If you really couldn't, that signals a real communication problem that makes you an unappealing candidate. But far more likely is that you just preferred not to and decided that therefore the instructions could be ignored.
Uncontrollable verbosity and a disregard for specific instructions are not ways you want to introduce your candidacy.