Being able to define a default variable at a high level in the configuration tree is a huge convenience. Sometimes some extra settings need to be appended to the default (for example adding an extra command-line argument to an inherited Shell command build step). With the current variable override the parent configuration's value is completely replaced, mean any changes to the default must be duplicated in the child which is easy to forget/miss. A true/false toggle (default to false for backwards compatiblity) to "Append to parent value" would be extrmely helpful in our environment.