TortoiseHg is superior to TortoiseGit in many features. Would be a matter of changing a few lines of code to make a new TortoiseGit based on TortoiseHg, or it requires weeks/months of development?
It would definitely not be just a matter of changing a few lines.
TortoiseHg is intimately written against Mercurial. It doesn't just wrap around the command line client, it integrates with the core python code.
The entire program, from bottom and up, would have to be rewritten.
It is much more constructive to give the TortoiseGit team good feedback on what you would like see improved.