Hi there!
I have a very similar problem (actually the same…), but I cannot solve it by changing the number of dashes. For my project I use Intershop, which has its own scripting lnaguage called ISML. It is almost the same as HTML, but has some additional tags AND - most important - it has a syntax for server side comments (so these are not compiled and so they are not rendered to the client’s). These comments are <!— ---> with 3 dashes each.
So, I cannot simply change them to 2-dashed html-comments or add a 4th dash (would end up in a syntax error). For this reason I am looking for a way of changing or - even better - extending the HTML-syntax so it will fit my needs. In ST2 I simply changed the html-syntax-definitions, but in ST3 this is not possible that easily…
I would be very happy about any suggestions!