VBA Conditional Formatting to Grey Out Certain Cells in Target Row

I need VBA, not conditional formatting, for when a person selects a client and a specific test associated with that client to render certain cells in that row grey and locked. If someone can create easy-to-read VBA (for this dummy) and explain what each thing means for row 3, I can modify it for the other rows. Keep in mind that this is for a table, and that it will be expanding over the course of a year with added entries. To my chagrin and dismay, I've tried seven books and numerous Internet fora to no avail. I’ve attached the file. This is for Excel 2016.