This could be achieved by having unique tags such as "Mining expense" and "Mining sale" - however, these tags will likely not be used by many users and you can essentially achieve the same using other tags already supported.

I assume that what you want is to separate the costs and income from mining from all other transactions. In this case, you can use any of the other tags not already used such that the tax report will show the total sum for your mining expenses and income from selling hardware.

We are introducing many new tags in the upcoming new website scheduled for December, and I believe you will be able to do exactly what you want using these tags.

Keeping this request open until the new site is live, so feel free to provide more feedback later.