The functionality to set 'customWorkspace' has been added to agents to bypass problems especially in multibranch projects where branch naming follows 'gitflow' or a simliar approach. There branch-names are e.g. "feature/XY". This leads to default workspace paths aligned with job names and encoded by branch-api plugin to '...feature%2FXY'.
This workspace paths cause a lot of build tools to fail e.g. maven, ant, ...
As already stated without this override functionality by 'customWorkspace' this problem is not solvable which means eighter to dont use multibranch in such cases, do not use jenkins fpr such builds or hack the "branch-api" plugin to use a more not conflicting encoding.
My approach was hacking where i modified url encoding to some non url encoded approach
e.g. use 'x2F' and not '%2F'
With support of 'customWorkspace' it will be possible to set such path in pipeline and leave default be default.