If you just want to send to someone, please use FTB Essential.
Press a key (default : Right Alt) to send a firework rocket to ask everyone in the server to help you. And it will send a custom message. If you accept other's tp request, you will send a custom message.
You can modify the message in client-config file. The message is a Component.
You can generate json messages from https://minecraft.tools/en/json_text.php
You can modify the cooldown or shouldBroadcast in common-config file.
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