Is this permissible?

Works for me.

I do things like that all the time when I write, but I've no idea what the "rules" are about such things - or even the general consensus of the "publishing" realm. Be interested to see the responses you get. It definitely works well for me. (Though maybe put the action in italic?) Dunno...

Weatherby said:

Interjecting a verb like this:

A crowd had gathered. Some of them held lanterns, others had flashlights. One figure even carried—William shuddered—a pitchfork.

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Your usage is fine. In standard manuscript format it is indicated by two hyphens like this "--". It is variably called a dash or an em-dash. See link.

I believe what Word does is turn your two hyphens into one em-dash.

Weatherby said:

Thanks, I did utilize em-dashes. Microsoft Word combines them, but I think that there is a setting to turn that off.

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Yes it does. You can change that in the Auto Correct settings.