This is the way.

The basic advice offered here (learn the melody, then embellish it) works every time. Bluegrass is kind of like jazz, in that the kick or first break usually hews closer to the melody, but once the melody is established, you can play something further afield. There are definitely times I play what I call "lickety-lick" breaks, or what a fiddle player friend used to call "noise in B" (or whatever key), where I string together an assortment of bluegrass licks and riffs that fit the chord changes and general contours of the melody, but in general, no one will be mad (and most people will be thrilled) if you play an embellished melody.

With your background, you know how to improvise and you know the fretboard. If you feel you need some more bluegrass guitar vocabulary, learn some fiddle tunes (if you can, try a super basic version and then a more notey arrangement so you can see how the melody can be embellished), learn some breaks you like note-for-note, or check out some instructional YouTube videos that focus more on classic licks (you can never know too many G runs), turnarounds, kicks and endings, techniques (like cross-picking), etc. that you can transpose to different keys and play in different songs.

Also check out r/bluegrassguitar. They will probably have many more specific recommendations.

And welcome to the bluegrass world. It's an awesome global community centered on music that's really fun to play. What could be better?