Did the soldiers typically remove the trim as personal preference, or did the did the government stop applying the trim to get the jackets out to the soldiers quicker?
The US Army produced clothing as described in the regulations, including cavalry and light artillery jackets with the tape trim. To receive payment for assembling the garments, they had to pass inspection, demonstrating that they met the pattern. Besides the US Government clothing, the volunteer troops could procure tailored clothing if they preferred, or have a tailor modify government clothing, etc. etc.
What the soldiers did with them after issue was between them and their superiors (if they cared). See post no. 8 above, the image of the 1st Arkansas Cavalrymen with their mountain howitzers. A couple of the guys have the trim on their jackets, and some of the others don't.
Michael R. Cunningham's 2020 article in Military Collector & Historian delved into the subject in some depth.
Here's a reference from the article to Wilder's mounted infantry brigade receiving cavalry uniforms, and removing the yellow trimmings...
photographs, etc. suggest it was not rare for cavalrymen to do without the brightly colored trim too for whatever reasons.
the modifications were various. Some removed the colored trim entirely. Others kept some. Some kept a single fales buttonhole loop of lace on the collar, and others removed both. Here's one with the collar lowered, and the buttons and loops removoed.
The trim was just whipped on for decoration. Removal just required yanking it off at the least.
it might also help to recognize that there was no specific "regulation" uniform for US Volunteer troops, (the majority). They could wear their own uniforms, uniforms provided by their States (or subject to their States' laws, etc.), or uniform clothing purchased from the US Army Quartermasters. After 1861, the latter is what most did. It is well known that a large proportion of the Volunteer infantry never bothered to draw the uniform regulation dress coats for infantry. And in the same vein, if the volunteer cavalry drew the cavalry jackets, and modified them occasionally for active service, etc., that would not have been much different.
Only in March, 1865 was a federal law passed that required the army to provide the full clothing outfit of a regular army soldier to each volunteer soldier.
And immediately post-war, with the volunteer troops mostly being discharged, there was yet on hand a large stock of US Army clothing.