Is a crown replacement an easy dental procedure? I am super stressed.

I have two front teeth crowns and they look really nice and natural. I just went to the dentist for a cleaning and check up. He said one of the from teeth crowns has a cavity at the margin. I go for cleanings every 4 months and this was not seen 4 months ago. He said I need to have the crown replaced after a filling. I am super stressed and not sleeping over this upcoming procedure. I am worried about the new crown not matching the other front tooth crown. The dentist said it would match perfectly, but I am still concerned. He mentioned he would send me to the lab that is making the crown so they can match the color. Also, I am super stressed that about taking the old crown off and damaging the tooth underneath. Is removing the crown easy? My biggest fear is that there will be extensive decay and they won't be able to save the tooth and I will have to walk out without a front tooth. I work in a very public job and this stresses me out. The dentist never mentioned this, but my head goes to the worst possibility. The insurance person said they needed prior authorization first before they could schedule me as the insurance company may decide that a new crown is not necessary. If I have a cavity how can the insurance deny replacing the crown. Isn't it necessary to fill the cavity and replace the crown? Could this be because the cavity is very small and they will say to fill it without removing the crown? Is that an advisable? Anyone that can help alleviate my stress and any of my questions? I am greatly appreciative of any help? I want to mention I have great dental anxiety and this has been compounded by my regular dentist retiring and now I have a new dentist. The stress of dental visits every 4 months cripples me.