Apply the same deformation to a second volume

[malonejp]

I have some marked up points on an image volume (a T1). This my fixed volume which I will use for registration with Elastix. I have points of interest in this volume.

I register the incoming image volume, the moving, also a T1. Then I use Transformix to map the points of interest marked up on the fixed T1 to the moving. All normal so far.

I have a T2 nifti of the same head in the fixed space. That is, the fixed T1 and T2 are already registered with each other.

After the T1 elastix registration, I would like to bring the T2 into the same moving space without a second registration. That is, the T1 in the moving space was deformed into the fixed space and I have the result.0.nii and transform parameters file - and I would like to bring the T2 along for the ride for free, and bring it into the moving space using the same transform parameters.

This seems super easy, so I'm probably missing something stupid. Or maybe not? All the transformix operations in the manual seem to assume I want to go the other way, to transform from the fixed space to the moving space (and I understand why this makes sense).

Is it possible that this requirement of deforming two images cannot be done easily because it is simply not a common use case? Maybe I have to write code to do it manually myself?