It seems that it will be better for you to modify the format of exported data.
It will make the job easier to export the tags AND import them if it is your final goal.
For example you can target something like:
VM / Category / TAG
VM1 / Storage / SSD
VM1 / Owner / Finance Department
VM1 / Performance / HIGH
VM2 / Owner/ Human ressources
Maybe you will need to export two CSV files.
One is for all VM information with a relation one to one like Name/CPU/Memory etc.
The other will contain all information for tag only which is a one to many relation.
A VM can have one or multiples tags on multiples categories (Or in the same category) or no tags at all.
With information in the format provided above you can reimport tags by working line by line.
The chapter “Data Normalization” in the book “Access 2013 Bible” is providing many concepts similar to the above that can be reused for manipulating data with PowerShell.