The max. allowed time to keep the slots unused is two months by system design. So you may not keep the slots reserved for 10 months waiting aircraft to be delivered.
And really coding it to the system is not that simple what you make it sound. There is already the automatic removal for unused slots (removed if not used for two months) but having an automated system detect possible changes in the routes and other tricks is practically impossible as there are so many variations and possibilities on how to cheat there. But perhaps you have suggestions on how to make it.
Like THI, I also schedule my flights before they come up as being available for actual 'scheduling' - this is due to work commitments, etc. I only do this for one or two aircraft at a time.
Secondly, if you change your flight schedules and dont have space for a route, can you just leave the flight in suspension till you have capacity or is that also considered slot hogging?
These cases what I've posted here have involved more than just 1-2 slots, so for "normal operations" there is no need to worry. The prescheduling vs. routes isn't also that clear, there is no set date when you can do it since it depends on how you can visit the site and so on like you said. But like I posted; if you do it some weeks before the plane arrives it is OK but doing it MONTHS in advance cannot be considered normal ops anymore since in that case you are restricting other airlines by reserving the slots too much in advance.
And for second part, there is the 2 month limitation on which you can basically keep the existing route and slot inactive - after that the slot is gone, so I believe this is also a good baseline for these types of changes.