Encumbrance due to use as a garage/ancillary facility?

Hello,
the following initial situation:
3 independent plots A, B, C located from north to south. Plot A has been in my possession for many years with a house, garage and garden. Plots B and C are each half developed with a semi-detached house in shell construction. I have now acquired plot B and want to convert the semi-detached house into a garage/outbuilding. Plot C is used as a residential house by another owner.

The building authority now wants plot B to receive a building encumbrance [Baulast] from A because of its use as a garage. The concern is apparently that I might open a business there, which I do not intend to do.
Are there any disadvantages from the building encumbrance besides the fee?
What would happen if I merged plots A and B?

Thanks and regards

Sorry, that sounds a bit too abstract right now with this XYZ without an image.

Sorry, but if this is too much, then C can also gladly be left out because it doesn't have any influence on the situation anyway... ;-)

Are there any disadvantages from the Baulast besides the fee?

In NRW, an official site plan would then always be required for future projects requiring a building permit. I don't know how this is handled in TH.

What would happen if I combine plot A and B?

Then you no longer need a Baulast.