Plenty of writes now works and an expanded example exists in the terraform directory

terraform/terraform.tfvars

@@ -0,0 +1,10 @@
+# Matches what's currently live on the switch, so `tofu plan` shows no
+# drift -- port 5 has a manually-fixed 100 Mbps Full Duplex speed
+# (AutoNeg Status=Disable in port_summary), ports 1-4 are Auto.
+ports = {
+  "1" = { admin_mode = true, link_speed = "Auto" }
+  "2" = { admin_mode = true, link_speed = "Auto" }
+  "3" = { admin_mode = true, link_speed = "Auto" }
+  "4" = { admin_mode = true, link_speed = "Auto" }
+  "5" = { admin_mode = true, link_speed = "100 Mbps Full Duplex" }
+}