It is not advisable to varnish over either of these two finishes. Often the adhesion of the varnish is massively compromised and therefore all traces of such finishes should be removed with either Wax Remover or Furniture Stripper
Yes you can use Colron Finishing Wax over oil, providing the oil has fully cured. Refined waxes are not suitable for this application.
Yes you can apply a clear wax over for protection, but not an oil.
Yes, However you will need to apply the required level of protection afterwards, Using Ronseal Diamond Hard Floor Varnish.
No, once the wood is stained or dyed dark it can not be lightened without removing the existing treatment.
Do I need knotting solution under a dye or oil? How long do I need to leave knotting solution before I can apply a coating on top?
Colron Knotting Solution should not be applied before a dye or oil as it will affect how the product is absorbed into the timber. After applying Knotting Solution an undercoat or suitable paint can be applied, wait until the product is totally dry.