We are transitioning to Shopify and have custom SKUs and Barcodes that have letters or periods or dashes in them. Is this not acceptable for Shopify?
SKU's are great for keeping track of your products but be careful what you include. Letters, numbers, dashes (-), and underscores (_) are great as they make SKU's more readable.
However, periods are not recommended (although they can be used) as they may not work with any other linked software.
Barcodes, however, are very different as they should be a new or existing Global Trade Item Number. Please read more here - https://help.shopify.com/en/manual/products/details#inventory
I hope that helps.
We have learned quite about not only SKUs but also barcodes. Barcodes can contain letters through the universally accepted Code 3 of 9 or Code 39. One can create barcodes easily manually or through an app or if necessary by registering a Global Trade Item Number. Please let me know if I can help.