Keywording existing files in LR

I have LR 5.x

I have some *.tif files that I created in Photomatix, completely outside LR/PS. They are not keyworded. I would like to keyword them and add them to my LR library, tagged/flagged, and so on.

Here's my question: After I import the *.tif into LR and keyword it, I suppose I will have to re-export it to get the stand-alone file to be keyworded, correct? I cannot imagine that LR would somehow alter the existing file automatically.

If they are tiffs, there is no need to export. After you have applied all the keywords, color tags, stars or whatever - either during import or afterwards in the Library module - simply do Ctrl+S or Cmd+S or go to the Metadata menu and select Save to File. For Raws (CR2, NEF, etc.) a separate sidecar xmp file is created, but for Dngs, Tiffs, Psds and Jpgs, the xmp metadata is embedded in the original file as a new subsection of the general metadata.