Altium de-highlighting nets after using 'Find Similar Objects...' command
To clear the selection of the Find Similar Objects use the SHIFT + C hotkey.


  After performing the edit, you will probably find that all the other
  objects on the schematic are faded out, or masked. While something is
  masked it cannot be edited, to remove the mask click the Clear button
  at the bottom right of the workspace [shortcut: SHIFT + C]. Page 4


And as for the footprint changes, I think the Footprint Manager is what you need.


  Altium Designer's schematic editor includes a powerful Footprint
  Manager. Launched from the Schematic Editor's Tools menu (Tools »
  Footprint Manager), the Footprint Manager lets you review all the
  footprints associated with every component in the entire project.
  Multi-select support makes it easy to edit the footprint assignment
  for multiple components, change how the footprint is linked, or change
  the Current footprint assignment for components that have multiple
  footprints assigned. Design changes are applied through Altium
  Designer's standard ECO system, updating both the schematic and the
  PCB if required. Page 12