Interesting topic. Your problem is obviously easily solved, just buy some black candles and consecrate your tool. On a purely psychological level, I'd always have the niggling thought in my mind that I really should have used some black candles, thus disturbing my own focus and the ritual's overall atmosphere.
Substitutions are another matter. Some time ago there was a question regarding a recipe from an old grimoire requiring mole's blood - ethical questions aside, how would you go about catching such an elusive animal? I suggested beetroots because they grow underground as well and their juice is blood red, too. Some rituals in the
call for animal sacrifices as well, and I've read accounts of practitioners fashioning clay figurines instead. In general, many recipes in ancient grimoire demand such exotic ingredients that you can't help but wonder if they're not blinds or even jokes; some of them used to be relatively common (parts of mummies were used in medicine in days gone by, for example) but are impossible to get hold of today.
Incantations: another tricky question. Sometimes you read adjurations that are downright Gothic-kitschy, sound like a nursery rhyme or slightly rub you the wrong way. I'd say it's ok to change an adjective or replace or omit a clumsy sentence here or there as long as you leave the
alone:
Change not the barbarous Names of Evocation for they are sacred Names in every language which are given by God, having in the Sacred Rites a Power Ineffable. (Chaldean Oracles 155, also GD Practicus Ritual)
Are you allowed to translate incantations? Asenath Mason is Polish so in which language does she conduct her rituals? The grimoires were originally written in Latin or Old German, for Psalm magic you'd strictly speaking need Hebrew, and as far as the PGM are concerned, there have been discussions here as to correctly pronounce Demotic Koiné Greek (answer: nobody knows). If you leave them in their original language you don't understand, you'll end up with
nothing but barbarous names in a ritual you'd be hard put to learn by heart, so in these cases translations are as good as unavoidable.
My own assumption is that a ritual only works if you are able to perform it with 100 % conviction and genuine heartfelt emotion; anything that stands in the way of fullfilment of these criteria should be modified or eliminated.