Can I switch visa category while in the UK?

Yes, it would make a difference. You would have had to entered the UK, temporarily, as an entertainer, in a category which is usually for those who are performing at a specific event, a one off, or over the course of just a few days. Entering the UK to visit family and, once in the country, asking to switch implies that you intended to, or have, found employment and now wish to remain. Officials may be inclined to think that you were not forthright about your plans in the UK, altogether not a good idea.

If you have the entitlement to switch to a specific visa category, you can generally switch from many categories into the new category.

Restrictions on switching are normally made clear in the guidance for the new category. For example, you cannot switch into a Tier 2 (General) Visa from a Standard Visitor Visa while you're in the UK: https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/791035/Tier_2_Policy_Guidance_03_2019.pdf.

If you're switching to stay with a family member such as parent or spouse, I don't think you're barred at all: https://www.gov.uk/uk-family-visa