xcrossi,
You are doing things the hard way.
If you want to change a batch of assets from one TB to another there are several ways that are more efficient than the manual method you are using.
METHOD 1 - REPLICATION
In any of the assets that you want to upversion or regress change one of them by using Outline (top left pane) trainzbuild by right clicking on its value.
This will open a text editor with a drop down menu with the values you can use. Select the one you want then OK.
Go to asset pane (top left) and click on another asset. This will open a window in which you can save what you have modified so far.
Continuing in the Asset Pane you need to tag all assets that you want to modify to the same state as you modified the first asset. If you are doing all you have OFEd then highlight one of the usernames (NOT the box) and then use shortcut CTRL+T. This will select all assets. You only have a choice of all (CTRL+T) or none (CTRL+U). You can individually tick each assets box and select them individually but obviously that is slow and tedious if you have OFE a large number of assets. You could control that by selecting only those you want to modify in CM prior to OFE.
Having made your selection in Asset Pane go back to Outline pane and tag the Trainz-build entry that you initially modified. Finally, and as long as you are sure you have got that right and only the assets you want to modify are selected in Asset Pane, LMB File\Replicate to tagged assets.
The white square between the Asset and Outline panes will turn into a circle which progressively turns black, reverting to a white square when the batch has been completed.
You now have all your selected assets at the new trainz-build value.
Return to CM and commit. Voila!
This is very fast.
Initially only do small batches by this method. As long as you are confident that you have the method sussed then the number of assets in the batch can be increased. I've done as many as 8,000 where just a simple change like this does not have consequences fo different kind.
METHOD 2 - OUTLINE TEXT EDITOR
If you are hesitant to use the REPLICATION METHOD then this method may be more to your liking.
As you did for the first asset in REPLICATE METHOD change each asset's trainz-build saving after each modification.
When completed the last one CM Commit.
Not so fast but probably up to 10 per minute depending on your proficiency.
METHOD 3 - TARDIS BATCH
Shortly I will be updating TARDIS to TARDIS 3.7.
In Asset Pane tag those assets you want to modify as above.
On AssetX menu Scripts\Run Script on Tagged Assets. This opens a window from which you select TARDIS REPAIR then TARDIS SCRIPTLETS then 03_Trainz-build. Choose either Up-version or Regression and finally select where you want to end up.
This method has an AssetX automatic save between each asset modification, so when complete CM Commit.
Fast. In excess of 3 per second.
The longest part of any of these methods is due to CM OFE/Commit processes.
METHOD 3 is used extensively in TARDIS 3.7 to navigate to a particular script and then carry out the modifications automatically, or where all actions are not possible to automate provides semi-automatic assist.
There are SUPERSCRIPTS like TARDIS Basic that carry out a plethora of repairs and changes to bring a multitude of assets into compliance unattended.