The 2nd line of your code is not functional python code. The ... needs to be replaced with wherever you are getting the transform node from. Simplest is to create it. Assuming your model node is named rcm_1, the following code should work.
import numpy as np # need to import numpy before np.array will work
transformNode = slicer.mrmlScene.AddNewNodeByClass('vtkMRMLTransformNode', 'myNewTransformNode')
transformMatrixNP = np.array(
[[0.92979,-0.26946,-0.25075,52.64097],
[0.03835, 0.74845, -0.66209, -46.12696],
[0.36608, 0.60599, 0.70623, -0.48185],
[0, 0, 0, 1]])
# Change transformation matrix in the transform node
transformNode.SetAndObserveMatrixTransformToParent(slicer.util.vtkMatrixFromArray(transformMatrixNP))
# Apply transformation to the model in rcm_1
rcm_1.SetAndObserveTransformNodeID(transformNode.GetID())
You mentioned that your segmentation is an imported STL model and this code will work for that. Note that in Slicer, not just models, but also segmentations, images, and markups can all have transforms applied.