Re: call component function only possible via interface?
I think you mean the <script> tag, and you should be able to call any of the functions in an included .brs file in your init, and while an observed field is, I think, necessary to initially call a function within an included file, I believe that called function should be able to call anything else within files included via the script tag. So if your onChange callback is a function named "DoSomething" -
function DoSomething() print "something" doSomethingElse() end function
function DoSomethingElse() as integer print "something else" return -1 end function