How to Create Additional Google Play Account Under 1 Google Account? I have just set up new Google Account on my tablet that uses new Google Play account. I want to add another Google Account that I use as main that already has history of apps I bought in the past and payment method associated with it.

So instead of using new Google Play account with no track record and bought apps, I want to remove it from existing Google Account and link to it established Google Play account.

How to do that without adding another Google Account to device only to have everything synced and mixed up? After all this is short term purpose because after adding apps I already bought, will mean removing that Google Account and switching back to previous. What if I want to download paid application again? Here we go again..
You have a very strange use case, and Dan Hulme's duplicate suggestion is actually correct. 

If you want to use the apps from an OLD account, you need to add the OLD account, switch to the OLD account, and install the apps through the OLD account. Then, you switch back to the NEW account, and remove the OLD account. If you want to install a new app from the OLD account, you need to repeat the same procedure.

As I said, you have a very strange use case, and this is the only workaround. If what you wanted were possible, it would be open to abuse. You could share the account to several people, and let them install apps using that account.

EDIT #1: As per Izzy, removing the OLD account can break the installed apps, as the license checks will fail. So, best to keep both OLD and NEW accounts, but disable the sync on the OLD account (as you suggested).