Smooth captions to match retro style video

I have a kinda grainy, retro style video I want to add captions to and match the vibe. However, when I add the captions, they currently look very slick and 'hi res' compared to the mottled look of the video.  Is there a way to smooth, or decay the captions without applying that filter to the entire video? (The video already has that look and I don't want to over cook it).  Thanks!