Yes, for example you can simply prefix the hotkey with a tilde:
~mbutton::
sendinput ^{v}
return
Which makes the hotkey non-blocking (lets the event pass further).
But generally it is not a good idea - it means you will have a system-wide shortcut which lets the application consume this event as well.
E.g. in Chrome, if you have an active input cursor in some form, then clicking m-button on some link will paste the text into the form AND open a new tab. In case of opening a link it might be actually ok, but imagine if some other software has e.g. "select all" bound to middle-click or something like that. So it should be used with caution.
IMO a better idea would be to make some application-specific script. This can be made with the #if
directive. See Context-dependent app . So for example you could have a hotkey only when Chrome is active and further check whether in Chrome you have input cursor active or not (might be possible, but I am not sure).