How to migrate to a new site

We have a rather messy site with CB and CBSubs and a collection of other extensions. We would like to migrate to a new site. We have built the new site which has a rather different structure using a T3-based template and CB/CBSubs.

I think the conventional way to migrate would be to clone the site via a backup and then add/replace the new template and then to delete/replace articles, menus, etc. However I am being asked if we can somehow do this the other way round - transfer the user/subs/etc data only from the live site to the new prototype site which already contains articles/menus/CB/CBSubs/etc

Thanks for any help you can give us on our site upgrade..

Are you migrating from CB 1.x to CB 2.x or is this an existing CB 2.x site that you just want to move the data?

If it's existing CB 2.x site the easiest approach is to likely export the users via CB Juice and import them back in. Next just export all the _cbsubs and _comprofiler database tables and import them into your new site. From there you'd just remove any database rows you don't want (e.g. remove plugin rows for plugins not installed) or ensure your export properly exports only the rows from various tables that you want.

Basically if the user id is unchanged from 1 site to another you won't have much issue directly moving CB/CBSubs data. The same applies for CB plugins and their respective fields/tabs as those are linked by plugin id. Then you've various parameters linked by field id so you'd want those fields ids to be the same, etc..

Thank you.
The old site is completely up to date version-wise. It just contains lots of clutter/litter which should have been removed and much of the content needs rewriting. So from our POV, setting up a clean new site is attractive (and we've done it). So your solution is ideal if it allows us to move CB/CBSubs to it. The new site has 2 users and the old one 10,000. It's also linked to a phpbb3 forum via JFusion. So you are certain that we can line up the Joomla user IDs, the CB UIDs and the phpBB3 uids just by moving all the relevant tables?

What about other components like acymailing and a few others - do we just move their tables too after installing them on the new site? Or do we have to reconfigure other components/extensions from scratch?

If they're the same versions you can just directly export your tables and import them to your new site. IDs won't be changed in this case. The tricky part is if you made custom usergroups or view access levels as you may have issues with permissions being lost. Moving Joomla users themselves is already like 3-4 tables to ensure their usergroup mapping, etc.. is moved.

What about other components like acymailing and a few others - do we just move their tables too after installing them on the new site? Or do we have to reconfigure other components/extensions from scratch?

I don't know. I didn't develop those extensions. Once you've installed the extensions again on your new site it should be fine to just directly import your data back in since they're the same versions on both sites.