Map variable replacement

I am trying to use tags in my deployments and I have this in my
variable “BuildTag” {
type = map(string)
default = {
Env = “UAT”
Customer = “AZRR”
At the command line, I am trying to run this command terraform plan -var BuildTag={"Env":"CS","Customer":"AZRR"}, which works, but is it possible to pass in a variable the same you do with a non-complex type such as this?
terraform plan -var=“Customer=$(Customer)” -out=“out.plan”?