Disclaimer: While this post may be written in a way that it has to be this way or no way, note that this is purely my practice and my thoughts on the matter. You may disagree with what I have to say, but this is purely what I go by when it comes to my practice. You are free to do what feels right when it comes to yours.
Intent in magic is important. Intent itself is difficult to explain, but in spell-work, it is pretty much using a certain ingredient, or saying certain words, or drawing a certain symbol, with a purpose. Many witches and spell-casters believe that intent is really everything, and that is true to an extent. The intent is very important when it comes to correspondences like how I associate lavender for relaxation and divination, and rosemary for banishing negativity.
Intent, in spell-work, is when you use certain tools and basically assign them roles in the spell you are doing. These roles are called correspondences. If I want to perform a spell for relaxation, I might include lavender to represent relaxation since that is what I correspond lavender with. However, what is the point of ingredients? The point is that instead of draining yourself, you get energy from the ingredients to use in your spell. You can do a spell without any ingredients and have it work because of intent! This is why intent is so important. However, when it comes to ingredients and substituting, things can get wonky.
In spell-work, there is a reason the ingredient is in the spell. In my previous example, the reason lavender is incorporated in the spell is that I associate it with the spell’s purpose. This way, I can use the energy Lavender provides to get what I need. Also, instead of taking energy from it, some ingredients are used to amplify your own personal power. The point is, ingredients are to help you tap into external energies instead of internal. So when it comes to substituting ingredients, you should not look at the ingredient as a whole but look at the reason the ingredient is called for in the first place. If you were to replace sugar in a recipe, you would find something sweet because that is the original purpose!
Now, not substituting the ingredient properly does not mean it will not work! It can work nicely and the spell can be fine, but you would have to had put more effort into the spell. If for this example, I used a printed photo or sticker of lavender for the sachet, that can work! But I would have to put more energy to get the same effect as lavender. This is because the drawing does not actually correspond with what I need from the lavender, but simply reminds me of it. This can be good if I want something to focus on while I use my own energy to put my intent in the sachet, but that defeats the purpose of using lavender, to avoid tapping into your own energy.
To properly substitute ingredients in spell-work, it is important to focus on what the ingredient is actually for. In this more related example, the purpose of the lavender in the spell is to represent relaxation. Now, saying this spell I wish to cast is a sachet, let us say we do not have dried lavender to put inside. I now must ask myself what part of the lavender I find relaxing. Is it the scent? If so, I can replace it with a cotton ball anointed with lavender essential oil. If it isn’t, then there is no point, because even if I am intending to replace the lavender with the scent, I could be more productive. If the type of relaxation spell I am looking to do is rest, I might use a sleeping mask. Why? Because the sleeping mask represents the type of reaction I want, like lavender. This is easier, and more productive, than trying to substitute the lavender with something that reminds me of lavender. That is because I am not trying to replace lavender when I am substituting, but am trying to find what fits instead.
Now, in another example, some people may say “If you can’t get rain water, tap water is fine,” when they are talking about ingredients, but here I must disagree. Rain water has specific properties, and if those properties were not going to be helpful in the spell, then the ingredient should just call for water- not rain water! Now, if they say to use rain water to make moon water, then tap is okay because the main property will be from the moon. Normally when you use rain water, you don’t really consider where the water came from. Some do, but you can always find a new way to incorporate those properties.
I find that people are so caught up with replacing the ingredient, and they do not really focus on what the ingredient is actually for. This is very common when others use spells created by other spell-casters, and tend to not think critically about why ingredients are included. This has been a huge problem in my craft, and it lead to a lot of spells not working the way I wanted it to. Once I started making my own spells, I realized that the ingredients are there for a reason.
This being said, some ingredients should be replaced! If you are going to cast a spell, and the instructions call for sage to cleanse the space before hand, but you personally feel that rosemary or lemongrass will do the job for you in a way you prefer, do that! If an ingredient calls for coffee to wake you up, but you prefer another caffeinated drink like tea or soda, why not? The point is, do what feels right.
And if what feels right is to exclude an ingredient, do not feel pressured to replace it. Energy and intent can do wonders. But, if you do want to substitute the ingredient for something else, hopefully now you can think a tad more critically.