They make a manual rivnut gun too that’s like a big pop rivet gun that’s not too expensive.Would something like a nutsert work? You could attach a piece of steel with a nutsert centered on the opening for the coat hook to the back side of the bracket and then make a replacement clip that you can put over the headliner when it’s installed and bolt the clip to the nutsert. A couple sheet metal screws should be sufficient to hold the piece with the nutsert in place while you install the headliner.
REXBETI 14" Rivet Nut Tool, Professional Rivet Setter Kit with 7 Metric & SAE Mandrels and 60pcs Rivnuts, Labor-Saving Design, Extra 1/4-20 mandrel with Rugged Carrying Case https://www.amazon.com/dp/B07MVXN7LK/ref=cm_sw_r_cp_tai_sBzfFbX063JE5