In conferences, especially in computer science domain; is it ethical, accepted and legal to withdraw a submission before the results notification/announcement?
all conferences have their own rules, and may at any time reject the text to deduct that some of its rules were not met. Can be copyrigh, standardization of templates, etc. etc
Before receipt of acceptance intimation from organizers one can withdraw the submission. It is not unethical. After all it is the author(s) decide where their paper is to be presented even though acceptance criteria is not in their control! Parallel submission is no way advisable.
Journals typically have rules against parallel submission, so I would not recommend a parallel submission/withdrawal strategy. This makes the job for the organising committee harder than it needs be. You could risk being blacklisted by conferences if such a strategy becomes evident.