Is it OK to run HDMI, etc. through non-standard connectors?
High speed cables use shielding, twisted pairs and separation etc to mitigate intereference.
Each standard has a maximum length that helps ensure that it can deal with exepected background noise over that distance.
So, assuming that you are not using long cable runs, the connector you choose is a low loss type and you try and maintain as much of the original shielding/twists etc( eg do not expose 30cm of cable at your join) it will probably be ok.
But until you make the connector you are probably not going to know.