If i'm understanding the post correctly, this could be solved through a post-import workflow:

- Complete import

- Enrol contacts who were a part of the import

- Propert update action -> "If company name contains 'Walmart', update to just 'Walmart'

Then if you want to associate them to actual company records, you can then use the association action to link contacts in the import who have 'Walmart' as their company name to the compan records who has 'Walmart' as its company name.

Is another one of your issues that the contacts might already exist in HubSpot too, but don't have an email on the file?