That's the path I took to getting here. I was very fortunate that the Assessor was willing to take me on as a trainee, provided I did not resign my job at the Assessor's Office upon completing my training and did not take orders in the County I work for. Both were reasonable requests in my opinion.
I can't speak for your state specifically, but the WA DOL was willing to take my mass appraisal experience for my work log. I did have to only count the work I did after becoming a trainee, and I had to focus on specific areas in my revaluation cycles as opposed to throwing it all on to the log. I also claimed minimal hours on each parcel, as opposed to claiming the maximum amount allowed. Finally, I provided a mix of revaluation and new construction work to show a well-rounded picture of my experience. A lot of the questions they had for me when reviewing it revolved around our statistical analysis, market adjustments, and regression analysis.
It's absolutely doable if your State allows for it. You'll probably be held to a little higher scrutiny because they don't typically get a lot of work logs focused on mass appraisal.