I have a pipeline job which gets some string (choice) parameters.
along the pipeline I edit one of those strings, and later on load a groovy script file using the load step.

I noticed that the changes I made to the string hold just until the load step, and after that the variable somehow reverts back to the original value (as chosen when the build was initialized).

e.g.
parameter name: SomeParameter
parameter value: SomeValue

pipeline script:

echo SomeParameter
SomeParameter = SomeParameter - 'Some'
echo SomeParameter
load file: 'myscript.groovy'
echo SomeParameters

output:

[pipeline] echo
SomeValue
[pipeline] echo
Value
[pipeline] load
[pipeline] echo
SomeValue