One more update. I emailed customer service about being charged the $300 change fee (likely pulled from the "voluntary changes" section of the full fare rules) rather than the $199 change fee displayed during the booking process on the KLM US website. The response was that they couldn't help with "after-sales" issues and to call them instead or contact them via social media. I contacted them via twitter, and after a fairly lengthy back-and-forth in which I included screen shots of the $199 fee displayed during booking and referenced in one section of the fare rules, the agent said there wasn't anything they could do about me having been charged the higher $300 fee.

After thinking about it for a few days, I decided to file a complaint with the DOT, including screen shots of the lower change fee displayed during the booking process, the full fare rules, and my twitter interaction along with information about my original and reissued ticket. After the initial automated response, I received a personalized reply almost a month later, saying that the complaint would be forwarded to KLM. About three weeks later, KLM reached out to me, stating that the higher change fee was a mistake, and that they would be sending a check for $101 within the next month.

Interestingly, the same contradiction between the "penalties" and "voluntary changes" sections in the fare rules still exists for a random set of US - Europe KL economy light fares I checked as of today, and the website still shows the lower $199 fee as penalty when selecting an economy light fare option. For the corresponding AF fare, both sections consistently show $199.

So, if anyone else is in that situation of having to change a KL economy light fare US - Europe and is being charged $300 instead of $199, it might be worth following up with the DOT as well.