Total Terminal opens new tab separately in macOS High Sierra
It's time to move over to iTerm2.  It's highly unlikely a fix will be found in the wild because it doesn't make sense to do so.

It's no longer under active development.  From the About page on their website



SIP must be disabled to use.  (IMO), disabling SIP to get a non-critical app to function is not a wise path to pursue.  SIP adds a layer of protection to your system that isn't worth disabling for a terminal app.  From their web page specifically on SIP


  System Integrity Protection (SIP) is a new security feature introduced
  by Apple. That's good, but unfortunately it prevents TotalTerminal
  from augmenting Terminal. This article will tell you how to configure
  your machine, so that you can use TotalTerminal. Before you do this,
  it is important to get informed about what System Integrity Protection
  is, and what it means to turn it off. Technical details are well
  covered in SIP review on Ars Technica. Apple also provided some
  information here.


And finally, the note from the developer himself:


  Do you really depend on TotalTerminal workflows so much that you want
  to possibly lower your system security? Frankly, I'm going to stop
  TotalTerminal development because I have personally switched to iTerm
  2. It offers similar functionality to Visor and comparable features to build-in Terminal.app.


TL;DR

Total Terminal requires you to disable  security.  It would be counter productive to find/create/bodge a workaround when ultimately you would end up with an insecure system when there are already excellent alternatives (like iTerm2) that don't have this vulnerability/flaw/drawback.