There is no real change in planing calculation from V5.5 to V6.3
What has been introduced is capacity to automatically calculate planning in planning view.
Of course, this feature should be enabled only in project construction

Uncheck this option, you'll retreive exactly same behavious as V5.5
You may reverse to previous, but there is no "reverse database" script, so you'll work with v5.5 code on V6.3 database.
In most case, it won't cause any issue, except for table fields that have been renamed (thjere are some on products, compoenents and vesions) or deleted (there are none).
Then if you migrate back to V6.3 or later, you'll get many errors during deployment, but this is not important, as it will concern database updates that you always have executed.