Ubuntu is one thing…
Lubuntu 18.10 release-upgrades to 19.04 which is it's intended support path. Why do you not want to take that intended route when 18.10 reaches EOL on the 18th? (tomorrow).
No your 18.10 won't blow up on the 19th, and you can still use it for as longer as your hardware works, however without security updates, it could be a security risk if connected to the web, or files are transferred using other means (the risk depends on what you do, what you transfer etc).
Yes you can still use the 18.10 install media to install ten years from now, however some functions may not work (eg. you may have hardware that requires the addition of packages which are grabbed from the web; currently they are available at http://archive.ubuntu.com/, however soon they'll be moved to http://old-releases.ubuntu.com and thus the installer won't find them resulting in errors). You won't notice this if you have very basic hardware (that the install media can cope with), but either way - due to no security updates you should instead be asking yourself why you want do this this? and should you!?
Lubuntu 18.10's intended upgrade path was to 19.04 are covered in https://wiki.ubuntu.com/DiscoDingo/ReleaseNotes (the Upgrading from 18.10 section) however there is a caveat that i386/686 isn't possible there.
…but Python is another
The original EOL date for Python 2.7 was in 2015. They decided to move it out a few years, but only until next year. That means that this program you have will also be a potential security risk in short order.
Perhaps the best solution might be porting the program to Python 3. With
2to3, you should find this to be a relatively simple task.