Hello, is there a way of palm muted a chord in the chord grid ... struming only the beat..example ''E7 X X E5 '' ....I have enter the ''X'' on keyboard but all disappears...

Not sure about creating exactly the same sound as a palm muted chord, but you can silence the chords on intervening beats by applying a Rest on those beats. Follow the chord with a period (.) to create the rest, like this:

enter 'E7,E7.' in the left hand cell (1st 2 beats)
enter ',E5' in the right-hand cell (last two beats)

[E7,E7. ,E5]

Experiment with shots and holds as well by using 2 periods (shot) or 3 periods (hold)

The only way would be to make a palm muted Realtrack. Maybe someone can make a user track that is muted

At some point it boils down to either make one if one does not exist or play the track on the guitar. Any out there want to create a palm muted loop. That might work

You can create the pattern with 2 guitars one normal and one muted with 2 tracks in Realband you could also do in in Reaper you can mute beat 2,3 on one guitar and un-mute 2,3 on the other, using Direct Input guitars then add the FX to the output.

If you had RapidComposer you could easily do it with the Strum Pattern Generator, I could make up a track for you if you get stuck wav or midi:

Also Musiclab RealGuitars will follow BB chord track and create any pattern you like
MusicLab's RealGuitars

BB Chord Output

I could make one up from them if you like.