Purchases from the DLC will always be available for you to download and install without any additional payment (except for the download time and your ISP charges).
In Option 2 from my list you will need to download and reinstall all DLC and and DLS items if you don't have a user data folder backup. If you do have the backup then you will need to copy the backup into the new user data folder (it will
not have the same name as your original).
Personally, I would use Option 1 from my list above as it would involve the least work with no reinstalls needed. Just click the "Ignore Assertions and Continue" button (or whatever it is called) when the first Assertion message appears, You may get another beta update before the next retail version is released (which you will also get).
When the label "Release Assertions" disappears from the bottom left of the Launcher you will have the retail release. Then use the following steps:-
- go into Trainz Settings
- select the Install tab and the Change Trainz Update Stream link
- select Next and Next again
- select Change Stream
- the Path Stream dialogue box should show Trainz Plus Beta, from the drop down box select Trainz Plus
- select Done
- exit the Trainz Settings and exit the Launcher
- Restart Trainz