Is there an HDL to 1) Upload candidate Labels (setup) 2) mass assign labels to existing candidates

Summary:

Is there an HDL to 1) Upload candidate Labels (setup) 2) mass assign labels to existing candidates

Currently we do it manually both setup and when adding a label to a candidate,

Please can anyone share the HDLs to

1) add the labels in the setup (via HDL), We know the steps to do it manually

2) Mass Assign the Labels to candidates / for example add a Label of Java to all the candidate who have applied to a Requisition that has a Job of Java Developer / etc

In general How best do you use Labels and what are the best practices around it