Cancelling UCAS early application and re-applying

I'm applying to Oxbridge and my other 4 unis during the early application cycle but I don't feel too confident about passing the Oxbridge admission tests and making it to the interview round. If i don't make it to the interview round (which I'll find out by end of October) can I cancel my application to the other unis and then re-apply during the regular admissions cycle after making changes to my uni options and to my personal statement?
I think I could definitely improve my personal statement and also if i cancel then I could add a 5th uni option. Is this even possible? I dont want to cancel before finding out whether I passed the interview round though. PLSS if someone could help me out and let me know

You can only cancel and resubmit a new UCAS application within 14 days of applying.

Why didn't you just add your Oxbridge choice to your early application and leave your other 4 choices blank ta add in later?

It's rare for universities to make decisions on who to give an offer to based on PS alone.