Downgrade 4.7.29 to the latest LTS 4.6.37 - is it possible?
Is it possible? - Probably, with a lot of time and skill.

In most releases, there are changes to the database structure or table content determined by the files under CRM/Upgrade. To revert back to a previous version you could in principle work through all the updates between your current version and the one you want to go back to and reverse each change in your database.  So if a table had a column added, you would need to remove it etc.  If a column was dropped, you'll have a harder time adding it back as you may not have the right values.

A git diff to show the differences in CRM/Upgrade runs to nearly 10,000 lines (depending on what options you use), so you would have a lot to work through!

Upgrading is regarded as a one-way process. If you do have the time and skills to successfully revert, I'd suggest that is more beneficially put to use in fixing any issues you find in the latest release.