It is not possible to send a partially completed submission to the NHSBSA, unless you are waiting for a price to be confirmed for a new product (see help page titled 'Can I Submit a New Product Without a Price?'). The NHSBSA sets the required information for each submission type and so all the in-demand mandatory information fields must be completed before the submission can be sent to the NHSBSA.
This also applies to the current paper based system. Until the NHSBSA receives all the relevant data, they are unable to process and approve your product changes.