BLM could use some button consolidation

[Archwizard]

Most propositions are not realistics. Lay line and between the lines are 2 coldown, even if between the line is a short. one. You can scathe without condition, even if xenoglossy is up. Etc.

For combine 2 spell you have to create a capacity which change depending if you are under condition like the pvp talents. Exemple ice 4 become fire 4.

Thats say you can create simple macro for that, so players keep the choice to keep each spell on the keyboard or not.

As Seraphor stated, the capacity for many of these suggestions already exists in-game, particularly the dynamic skill replacement which is used by several other jobs like RDM finishers, SMN's Ruin, DNC's steps, AST's cards, etc; such methods simply haven't been deployed for BLM yet, even though they would be realistically applicable.
Meanwhile a majority of these suggestions are about combining buttons that are either mutually exclusive (like Fire IV and Blizzard IV, or Despair and Umbral Soul) or dependent upon one another (like BtL with Ley Lines, or the IV spells with Enochian), or outright trimming skills we already don't use because we have significantly better versions (the II spells, or Scathe).

transpose could turn some spells into aoe version and vice versa?
or a skill similar with the execution of Transpose

Transpose is fine as it is, honestly. It's the only oGCD method to keep Enochian going, on top of being the only reliable instant means to do so without popping CDs until we get Umbral Soul. Even if it's an absolute last resort at 80, it's good to have such a tool on hand.