Conditionally modify import statements

I have a collection of .py files in the following file structure:

packagename\
    mod_1.py
    mod_2.py
    script_1.py
    etc.

These files do two things:

1. They're bundled into an application (a JMP/JSL add-in, although not relevant here). In this application script_1.py is called, and it contains import statements like import mod_1. mod_1.py in turn imports mod_2.py as import mod_2. This is fine.
2. The files are also bundled up into a python package called packagename. In this context when I want to import mod_2.py inside mod_1.py I call import packagename.mod_2. This is also fine.

I presently implement this in mod_1.py, very painfully, as:

if 'addin' in __file__:
    import mod_2
else:
    import packagename.mod_2

This works but I've got lots and lots of modules (more than just mod_1, mod_2). Is there a way to do something like this (pseudocode)?:

if 'addin' in __file__:
    import_prefix = ''
else:
    import_prefix = 'packagename.'

import import_prefix + mod_2

This answer seems to cover half of what I'm looking for, but not everything:
https://stackoverflow.com/questions/12229580/python-importing-a-sub-package-or-sub-module

You may just want to use importlib.import_module.

import importlib

def _import(module_name: str):
    if 'addin' in __file__:
        return importlib.import_module(module_name)
    return importlib.import_module(f'packagename.{module_name}')

mod_2 = _import(mod_2)