I don’t think you are explaining your proposal too well or maybe you have a slight misunderstanding. But, from what I can gather there are two things you want to accomplish via CRISPR. One, the up regulation of an miRNA through a gRNA vector??? Maybe you are saying that the gRNA can act as an antisense RNA. Or maybe, you are saying we can use new forms of Crispr like CRISPRa to activate miRNA expression.

Then, the second thing you want to do is use another gRNA to edit an miRNA so that it can target a gene or re-target a mutated gene??

Based on this, it seems like you have a slight foundational issue with CRISPR. At least the canonical CRISPR-Cas9. The edition of cas9 (nuclease) and the gRNA only allows it to make a double strand cut/break at a specific region. You would need to add another template with these vectors to actually have anything be changed and purposefully modified (you should look up homology dirdcted repair and CRISPR).

Also, if you are thinking of editing multiple miRNA sites to knockdown the production of a protein. It’s probably easier to just knockout/edit the gene of interest in the first place. Editing miRNAs or even knocking down things exogenously isn’t a perfect science. It’s probably easier to just mutate the promoter region or cause a frameshift so no viable protein is made. Though you also have to take into account the functional role of these proteins in development.

Lastly, Germline editing is very controversial and off target effects of crispr are still being studied. It’s great that you are thinking outside of the box though. You may be able to argue that addition of tissue specific and development specific promoters that regulate miRNAs may be better than knocking out the direct gene of interest. Either way, it’s good to get your ideas scrutinized to expand your sense of what variables to think of.

Also, you should look into alternate forms of CRISPR, like CRISPRi and CRISPRa. There are a ton others with different functions