Create a custom line and move it into a custom palette.

After a fair amount of searching and combining bits of information from various posts and sections of the online help -
I added the below to my personal Musescore user / help manual,
in order to change Ped. to Sost. and have it available without having to edit it on the score every time.
(See attached image)

Move a custom line into a custom palette:
1) Create a Custom Palette by using the "Add Palette" button at the top of the palettes window. (F9)
2) Add a line to your score from the existing default lines in the lines palette.
3) Modify that line, after it's on the score, by using the inspector (F8).
4) CTRL+SHFT+Drag the customised line, from the score, into your new custom palette.