As the men who wear striped shirts on Saturdays say, "on further review" you may be right. Certainly the regiment organized as an infantry command when turned over to Confederate service on April 8, 1861. Other Alabama infantry regiments such as the 2nd and 17th served in the bay forts as artillery. It's somewhat difficult to discern the two services because officers usually signed as "1st Ala. Vols." or "1st Ala. Rgt.", never "1st Ala. Inf."
Dr. Owen thought highly of McMorries, never failing to mention his book to other veterans as a model for future Alabama regimental histories. However, as an enlisted man, I'm not convinced that McMorries knew as much about regimental organization as a field or staff officer would have. For that reason I was pursuaded by a document written by Col. Steedman in March 1862 which specifically designates his new command as the 1st Alabama Artillery. As secondary evidence, note that new Company "K" organzied in March 1862 as the "John Gill Shorter Artillery." Steedman's letter can be found in his service file, but I don't have a reference copy in my regimental files.
Your post prompted me to pursue one of my many unfinished projects, and they are legion. If Steedman's document has any meaning, officers would have received pay at a higher rate. However, a check of Captain Isbell's file shows that he continued to be paid at a rate of $130 per month after March 1862. That's the best test I can imagine. It could be that the War Department didn't act on Steedman's letter concerning reorganization, officers and men continuing to be paid as foot soldiers.
With regard to disbanding, officers and men of the old 1st Alabama Volunteers went home at the end of their twelve-month terms. Since most companies had organized in January and February of 1862, members simply went home. Many officers and men left with the understanding that they would collect new recruits and reorganize, but that was strictly voluntary. A break in service of about sixty days exists during which officers were not in commisson and the regiment ceased to exist.
That's my reason for saying the regiment disbanded. Nearly all regiments which had organized later were retained in service by virtue of the Conscript Act. If you have something to demonstrate otherwise, I won't mind be proven wrong on this point, either.