How do I deal with changing values in a categorical variable when I am aggregating customer records
The standard option would be to create one feature for each possible pair (variable, category) and use the frequency of this particular pair as value for this particular customer. If the number of times doesn't matter, it could be transformed into a binary feature, i.e. just indicating whether this customer has ever been seen with this category.

In case some categories appear very rarely, it's usually counter-productive to include them so you could have a minimum frequency in order to filter out rare pairs.