Yes, the H264 decoder does that all the time. It reports a type change right before the first frame is output.
Most of the time this is because native decoder has some 16-byte alignment requirements which always changes the 1920x1080 default frame size to 1920x1088 with 1920x1080 MF_MT_MINIMUM_DISPLAY_APERTURE attribute, but it also does if H264 streams are concatenated.
Note that this can in theory cause some transform connections to fail, if the downstream elements cannot accept the new upstream type, and I believe that there's more events and statuses that can come into play (for instance MF_SOURCE_READERF_ALLEFFECTSREMOVED is documented to happen when custom downstream transforms are dropped because of this), but it's not needed right now.
In practice, with the H264 decoder and a 1920x1080 requested source reader current media type, when the decoder reports its new type with a display aperture, the video processor still accepts that new input without changing its output type, by automatically cropping the buffer padding. This is currently broken in Wine, and the video processor will refuse that input type, and we will need https://gitlab.winehq.org/wine/wine/-/merge_requests/5055 to fix that.