… to customise the code to better meet your library’s needs?

… or to put up with bugs and awkward features until they’re officially fixed?

The former endangers a smooth upgrade path, and the latter fosters frustration for users.

Even if your library is lucky enough to have someone with the skills to customise the code, chances are that that person won’t always be around. And even the smallest of code fixes can seriously endanger the ease of future upgrades.