It’s inevitable. We all have patterns.
I find that I write certain kinds of songs with the guitar, and certain kinds at the piano.
The solution? I took a page from Stephen Sondheim’s playbook: I write melodies away from any instrument. He said he did that in order to not be bound by the limitations of his instrumental prowess.
After I’ve solidified the melody I’ll start chording & arranging. It helps keep me from following my hands’ patterns and allows more creativity in the writing process.