Do you want to ADD your secondary account? If so, go to setting, accounts, add new account, and simple sign in to that other Google account. I have my account, and my wife's account both logged into my Note 10.1 when you go to the store, just select the account you want to download an app from. Both her apps and mine are on the tablet, and we have full access to them all. Then we just customize our own panels on the dashboard. one for all of my apps, and one for all of hers. It has been working for 8 months now with no issues.
However - if you want to only use that secondary account, and not the original, you will have to sign out of the original fully, then sign in to the secondary - and yes - you will lose access to any apps that the primary is associated with.
Android 4.2 incorporated user profiles, similar to your PC: where each user can select their account and log in to the device to show their own dashboards, apps, etc... but sadly, the original GN 10.1 doesn't have, and will not get, this update. The only option is if you root the device and run a custom rom like Cyanogen...
I hope this helps answer your questions.