Hi Werner,

The first thing you can do is to ask the fontspec person to update the package :)
But of course you have a broader point:

> On 31 Jul 2017, at 11:53 pm, Werner LEMBERG <[log in to unmask]> wrote:
> To satisfy the LPPL I thought the right solution is to copy
> `fontspec.sty' to `fontspec-patched.sty', then applying the following
> change:

In fact, requiring a change to the filename is no longer written explicitly into the LPPL.
(Long story, don’t ever ask Frank how many emails it involved.)

You would be well within your rights to add something like the following to the top of your patched version of fontspec.sty:

    \typeout{This is Werner Lemberg’s altered copy of fontspec vX.X.}

The most important thing is that the altered code is clearly differentiated to the user as being altered from its original.

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A possible alternative to your problem would be to trick LaTeX into thinking that you had already loaded fontspec.sty.
This would be done with something like:

    \expandafter\def\csname [log in to unmask]\endcsname{}

(Look into memoir.cls’s \EmulatedPackage code for more details.)

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Hope this helps,