Could I substiture green beans in a bread & butter pickle recipe?
Maybe. But you should NEVER attempt to can or pickle anything (especially green beans- low-acid foods=botulism-or-worse) without first consulting the USDA’s website: http://www.uga.edu/nchfp/publications/publications_usda.html to gain a very clear understanding of the principles and equipment that are necessary for safe home canning and preservation. If you live in a Western (U.S.) state that has a land-grant university, free hands-on courses are almost always available through the extension office.