The SPS token holder community may submit and approve any proposals that they want, however the following guidelines should help to ensure that proposals are clear and that voting goes smoothly. The community is ultimately responsible for creating the guidelines that they want proposals to follow and enforcing them by voting against proposals that don't comply.
First and foremost, proposals may not be materially edited once the formal voting phase has begun. Minor updates or clarifications are generally fine as long as they do not meaningfully alter the details of the proposal. During the pre-voting phase, any changes may be made, and this is typically the time where the proposal author can gather feedback on their proposal and make changes that they feel will help the proposal to pass once it goes into formal voting. Any edits to proposal posts will be publicly and transparently recorded on the Hive blockchain so the community will be easily able to tell if any changes were made and what those changes were.
Proposals should also be as narrow in scope as possible in order to give them the best chance of being approved. If there are multiple changes being proposed, it is often better to split each change up into a separate proposal, as long as they are not dependent on each other. This gives the community the opportunity to vote on each one individually and would allow one change to pass even if another does not.
Finally, it is recommended that proposals be as clear as possible about all aspects of how any proposed changes should be made. Proposals with too much ambiguity should generally be rejected by the voters as it makes it much harder to implement and to predict the outcome of the change. If a proposal does not pass, the author (or anyone for that matter) may always submit an updated proposal that resolves any ambiguities or other issues that contributed to it not passing.