MOSAR is not law, it is a guideline, and one limited to Wikipedia at that. And frankly, "only if at least 75% of all references in English had used the spelling "Harun al-Rashid"" is a meaningless argument because you apply double standards.   Meanwhile, in the actual world, prevalent usage is both clear, and supported by the best of sources. Sorry, but "in my opinion" carries no weight when an array of first-class academic references is perfectly happy to use the "al-" form. Wikipedia follows usage, it does not create it. I sympathize with striving for phonetic accuracy in transliterations, but this is a case where usage is so overwhelming that this debate is pointless. Anyhow, long story short, if you don't agree with keeping the old name, this calls for a WP:RM.    ✍