managing locked and unlocked text in a vba textbox

I have a textbox named notes. On command button click the value changes to "ST(P) POC(Y) CR(1)" what i want is a way to be able to lock the default text except whatever is in Parenthesis editable.
What is want is that a user cannot edit the default value except whatever is in the Parenthesis.

Once that is done, i also want that if after the last parenthesis close a user enters anything, he is able to. Now if in that entry he enters a certain string like "`nmc" (in whichever case - upper or lower) then the default value changes to "ST("whatever user earlier entered here") POC(" whatever user earlier entered here ") NMC() CR(" whatever user earlier entered here)

similarly certain strings followed by "`" will need to add more default text to the already existing text which will have their editable text in the parenthesis

and if i need to remove that default (locked) text then i need to use `removenmc so that entire string from "nmc( to ) should go away.