Tumblr’s post editor doesn’t have a <code> button, but the monospaced typewriter font looks nice both in the dashboard and on my blog.
Both Linux and Mac OS X have a terminal or command-line which hooks into decades-old unix commands for processing plain text.
xsel -ob > the-post-im-working-onsed -i.′bak s#strike>#code>#g the-post-im-working-onxsel -ib < the-post-im-working-on
Or, cut out the intermediate steps of making a file and backing it up:
xsel | sed s#strong>#code>#g | xsel -ib
In Mac OS X it would be
pbpaste | sed s#strike>#code>#g | pbcopy
You may need to escape the > symbol to \> like this:
xclip -o | sed s#strike\>#code\>#g | xclip -i
You could also just search for s/strike/ rather than s!strike>!. But that would catch the actual word “strike” if you used it in your writing. (This is more of an issue if you use <em> or <strong> as demarcators. I do that when I want to insert <small> or <big> tags.) Whereas strike> catches either <strike> or </strike> only. (Especially since < and > are encoded as < and > if they’re used in text—so the > is really mostly likely to only catch HTML tags.)
I don’t know if this can be done in Windows PowerShell. It either can’t be done in a GUI at all, or it would be more cumbersome to do in standard point-and-clicks.

