Possible to import prewritten code?

I am not sure if what I’m envisioning is possible, but I am not referring to the listings package (which is what all of my searches are yielding).

I reuse a lot of my LaTeX code. I recently figured out how to replicate large parts of my preamble (which has over a dozen packages and user-defined commands) by making a single "custom" package which I call in my documents. However, there are parts of my preamble that I also reuse but have change small parts of in each document.

For instance, I have the style of my title page defined, but the title itself, the date, etc. needs to change. Is it possible to do something where I put my code into another document and call it in each document with some parameters? For instance, if I put everything in a class called mytitle and then call that specific package in my document:

usepackage[title,subtitle,author,date]{mytitle}

where those options are defined in the package itself?

I thought that classes would be the right option, but it’s looking like that isn’t the right solution.