...in other words, if you're working with a SSIS package using Package Deployment model, first set up the package so it uses a .dtsConfig file that contains the username and password for your connection manager. Then, using BIMLExpress, convert your package to BIML. BIMLExpress should create the BIML file with the appropriate info and XML elements for the package to use the .dtsConfig file. When you then regenerate the the package from the BIML file, voila, SSIS will then configure things on whatever is in a given .dtsConfig file.