I stumbled across this trick when changing a large city's maxis street's to one of the SAM textures, on several plop attempts I managed to incorrectly place the SAM starter piece and bang one immortal lot.
No1: Ive placed the maxis jail (but have used this method on all my immortal lots)
(https://www.sc4devotion.com/forums/proxy.php?request=http%3A%2F%2Fimg135.imageshack.us%2Fimg135%2F3681%2Fimortallottutorial1.jpg&hash=9573588c41b24d12537781063beee4ea36ca0213)
No2: one immortal lot.
(https://www.sc4devotion.com/forums/proxy.php?request=http%3A%2F%2Fimg137.imageshack.us%2Fimg137%2F5374%2Fimortallottutorial2.jpg&hash=3c38667a997de3e1ea3ba83eaeacfa6748ba3e5c)
No3: The lot is immortal and no amount of clicking will remove it.
(https://www.sc4devotion.com/forums/proxy.php?request=http%3A%2F%2Fimg560.imageshack.us%2Fimg560%2F2096%2Fimortallottutorial3.jpg&hash=d3340d28ee63405e0b69535e0ad02dc836e26279)
No4: Now for the trick using the low density residential zoning tool draw a road through the lot use the bulldozer tool to delete all the roads and the immortal lot should highlight red.
(https://www.sc4devotion.com/forums/proxy.php?request=http%3A%2F%2Fimg718.imageshack.us%2Fimg718%2F6858%2Fimortallottutorial4.jpg&hash=e6ff3890de2372c0db633054f3c2c25817438a77)
No5: Use the bulldozer tool to delete all the roads (the immortal lot should highlight red).Then De-zone the unwanted residential zones and the land is yours again.
(https://www.sc4devotion.com/forums/proxy.php?request=http%3A%2F%2Fimg715.imageshack.us%2Fimg715%2F5250%2Fimortallottutorial5.jpg&hash=3976f3895304a7f1cbab7aebc5c2a603b819fbdb)
Hope you find this as useful as i have.
Mark
THANK YOU! I tried everything to get rid of an "immortal" train station and was about to revert to a saved city version which would have caused me to throw away hours of work. Your solution was magic.