Can custom dimensions be added for Piwik? Currently custom variables are supported but they are being deprecated per their documentation. Custom dimensions are limited to 1000 whereas custom variables are limited to 5.
Please reference https://piwik.org/faq/general/faq_21117/
"In general we recommend users to use Custom Dimensions as we will deprecate Custom Variables at some point. With Piwik 3.0 Custom Dimensions will be most likely installed by default."
This isn't something that the tag template currently supports but it is on the tags roadmap to be updated with. In the mean time you can use a scoped extension to set any custom Dimensions that you wish to use with Piwik.