Can I change the variant names like Size, Colour and SKU?

For the Colour and Size, yes, you can change it. Some scenarios for changing include wanting to provide a different colour name (ie 'Mystic Blue instead of Blue). Or, where the product might have 'White' colour but your design changes that. This is generally applicable to edge-to-edge printed goods like dye-sublimated face masks.

Example of changing the 'Colour' name of the face mask from White to 'Lemon Print', to better represent the design/colours of the product. 

For the SKU, no, you can not change the SKU, as this is the unique identifier required for OGO to synchronise your inventory and products. Changing the SKU will affect real-time updates of inventory, and potentially fulfilment of any orders with the affected products.

After your product is created by OGO, and published to your store, you can edit any of the product details

Variables you are welcome to edit include

• Title
• Description
• Images (replace or add images)
• Variants
  • Size
  • Colour
  • Price
• Vendor

What you should not do

• Add your own variants, such as a new Size or Colour, via Shopify Admin Products section. If you wish to add a new colour/variant, go back to the OGO app and edit the product through the OGO App. Variants that have been added manually and not via the OGO App aren't linked to OGO, and therefore won't be tracked.
• Delete variants, even if there is only one variant for a product (ie Tote bags)
• Edit/Change/Delete the variant's SKUs
  
  Modifying the SKU will affect the link between the product and OGO. It will cause issues with inventory and fulfilment. DO NOT EDIT/CHANGE/DELETE the variants SKUs.

Things to Note (IMPORTANT)

If you edit your product again via the OGO App. It will essentially recreate the product from scratch, and override ALL changes you made to the product except the Title and Description. ie, if you replaced or added images in Shopify Admin's Product edit, these will be removed/replaced with the original OGO images.