Extend methods from another module while calling the original method within the extended method

One option:

julia> module Foo
         myfunc(x) = println("Foo original");
         end
Main.Foo

julia> import .Foo.myfunc as foo_func

julia> foo_func(1)
Foo original

julia> myfunc(x) = println("Extended", foo_func(1))
myfunc (generic function with 1 method)

julia> myfunc(1)
Foo original
Extended