Tips and Tricks
The Classic WoW variants do not have Retail's spec APIs. This means that GSE can't swap sequences based on the spec chosen. There are a couple of different techniques that can be used, but the simplest way is to test if an ability is known using an If Block.
The API IsSpellKnown() will tell you if your player or pet knows a spell. It is documented https://warcraft.wiki.gg/wiki/API_IsSpellKnown. In the screenshot, you can see how this is used in the Variable part of the IF block. 20928 is the Spell ID for Holy Shield, which this paladin doesn't know in this spec. If I put the Prot stuff into the True side, I can then put the Prot Sequence into the false side.
This technique can also be used in Retail. More information on IF blocks is located at https://github.com/TimothyLuke/GSE-Advanced-Macro-Compiler/wiki/GSE-3.2-Block-Specification#if