I have added the Plikington English Red & Pre 64 spirit stains & sometimes a bit of the Pilkington red brown rubbing oil to the clear Pilkington finish (also to Tru Oil for quick touch up although I really don't like Tru Oil) to get the color I want. Note that the red/brown rubbing oil will significantly increase the time before it gets tacky (a plus w/Tru Oil for me).
You will note that the instructions for the Pilkington finish suggest thinning it anyway although they also say you can use it straight. I've only used it straight when I wanted a built up finish.
I've not had any issues but you are on your own here. I'm not sure what the "spirit" is in the Pilkington Stain but it must be something close to lacquer thinner as the stains will temporarily soften some finishes if used for touch up so careful handling is required.
