I'm planning to activate a local lighthouse this coming ILLW in August. Here's more info.: https://illw.net/index.php
You have at least two possibilities. The first is to put your call sign W6AJR/LT into My call: in the General settings. Unfortunately that generates certain limitations what you can do. There is no place for locator in the messages and you cannot work other stations using “special” call signs. Also one of two call signs in message will be in short form indicated by angle brackets <W6AJR/LT>. It may disturb, but all is working.
The second is to “broadcast” your special call sign as a Tx5 message such as DE W6AJR/LT. That may generate logging problems to some operators as they will not know whether you will record e.g. into LoTW as W6AJR/LT or just W6AJR. Another variant DE W6AJR /LT (note space before /LT) may be better and it fits into free text. By the way you may store that message, if you type it into Tx5 and complete typing by Enter. It will be available in the drop down list.
73, Reino OH3mA