sed-multiline

if [[ "A" == "A" ]]; then
    sed -r "s/^(#)?labels=.*/labels=PROJECT:Venice;SERVER-STACK:${APP_NAME}-${ENV};\
EC2-TYPE:${INSTANCE_TYPE};VPC:${VPC_ID}/" newrelic.cfg | grep labels
fi

if [[ "A" == "A" ]]; then
    sed -r "s/^(#)?labels=.*/labels=PROJECT:Venice;SERVER-STACK:${APP_NAME}-${ENV};\
    EC2-TYPE:${INSTANCE_TYPE};VPC:${VPC_ID}/" newrelic.cfg | grep labels
fi

SED_REPLACE_EXPR="labels=PROJECT:Venice;SERVER-STACK:${APP_NAME}-${ENV};EC2-TYPE:${INSTANCE_TYPE};VPC:${VPC_ID}"
SED_MATCH_EXPR='s/^(#)?labels=.*'

if [[ "A" == "A" ]]; then
    sed -r "${SED_MATCH_EXPR}/${SED_REPLACE_EXPR}/" newrelic.cfg
fi

SED_REPLACE_EXPR="s/^(#)?labels=.*/labels=PROJECT:Venice;\
                  SERVER-STACK:${APP_NAME}-${ENV};\
                  EC2-TYPE:${INSTANCE_TYPE};VPC:${VPC_ID}"

sed -r "${SED_REPLACE_EXPR//[$'\t\r\n ']}/" newrelic.cfg