How can I create parameters at the Project/Global level in SB

In your NameMap, change the URL of the Page objects to use wildcards.  So instead of

http://dev.mycompany.com/test.html

http://qa.mycompany.com/test.html

you have

http://*.mycompany.com/test.hml

See Using Wildcards in Name Mapping

In your tests, you'll need to construct your URLs.  You might create a Project variable to contain either "qa" or "dev" and then construct your URLs using it:

testURL = "http://" + Project.Variables.source + ".mycompany.com/test.html";

Aliases.browser.toURL(testURL);

See Project And Project Suite Variables