We should definitely swap the cleric domain. But I don't recall having any other justification when we swapped the Mystaran amber's SLAs around.
In the case of the Amber, it seemed pretty clear the Gold Dragon's
bless and
sunburst SLAs weren't terribly appropriate for a BECMI Chaos-aligned monster, so we gave them SLAs that were more in keeping with that ethos. For example, rather than a glorious radiance that annihilates undead (
sunburst) it produced a radiance that destroys matter in general (
disintegrate). I'd have been OK keeping the Gold's
quest/geas, since you can see that being used in service of malevolent Chaos.
Also, we don't have the clear alignment inversion the Amber & Gold dragon's had, since Golds are Lawful and benevolent in both versions. The Blue Dragon is
already Lawful in AD&D and 3E, albeit Evilly lawful, while it's Neutral in BECMI.
Anyhow, what alternative spells would you fancy?
The Blue Dragon's
ventriloquism,
hallucinatory terrain,
veil and
mirage arcana SLAs all have a clear Illusionary theme that doesn't seemed tied to the concepts of Chaos and Law as BECMI represents them.
The AD&D/3E Blue Dragon has a Lawful Evil alignment, so if our Azure Dragon is a "good" inversion of that it could have SLAs that are benevolent mirrors of the Blue's spells - maybe something that reveals the truth rather than cloaking it in illusion?