UCL Postgrad Uploading documents to clear conditions without accepting the offer?

Hello! I have conditional offers from two UCL MSc programs and I was wondering if it’s possible to upload the documents to clear my conditions without accepting the offer?
I wasn’t able to meet the condition on my grades for my first choice but I want to upload the documents and a written letter about some extenuating circumstances. At the same time, I want to hold on to the conditional offer from my second choice ( I meet the conditions fully) just in case I get rejected from the first one.
Is it possible to upload my documents to clear my condition without accepting the offer?
If it is, would I be able to upload the documents for two programs at the same time?
If it is necessary to accept the offer before uploading the documents, would the second offer be rescinded once I accept one?
Since I am an international student, it would be great if I could upload the documents for both programs and have them processed simultaneously, in order to move on to the visa and accommodation application as soon as I can.
On my portico, I have the ‘upload document’ tab on the top of the application page and the message that says ‘We require you to upload additional information. This may refer to the conditions in your offer or to a further email from us. Please go to the Upload Documents link above.’ for both of my programs.
Can I get any advise on what the best course of action is in this situation?
Thanks in advance!!