If a tenant is sick and contagious, do they have to allow landlord owner in for appraisal or can the tenant reschedule?

If it is just for an appraisal then the landlord might not be in any great hurry and it would be unreasonable to let a person who is well in. But appraisals go very quickly so it probably is better not to get into an argument with your landlord. If you will be sick for a long time, he could come in at a reasonable time. Technically, he might not be able to come in for an appraisal to get a new loan, but I would not argue the point.