Is it possible to use the remesh node only on some part of the mesh, like what we can do with the group node hooked to the input components?

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Not internally.
I remember debating with myself if i should add this functionality, but there were couple of reasons that made me vote against it:
- possion reconstruction does not match original mesh boundaries
- same for isotropic remeshing
- topology can match bounadaries
- unordered point cloud does not match them
As a result only one of the 4 methods takes advantage of component lists in an useful way.
So i decided not to implement that and leave it to the user to use group + delete to isolate list of components that need to be remeshed, then merge back if needed or applicable.
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ok i see thanks 
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