If you want or need to make a substitution in a crochet pattern (whether in yarn, technique, or any other modification), the first thing you need to know is this:
There is no right or wrong in crochet! If you’re happy with what you’re making, then yes, you can make any changes you wish.
If you’re not sure if it’s going to work, I encourage you to test it out – you don’t need to make the entire pattern, just choose a small piece and crochet enough of it to see if you like the look and shape of the fabric you’re forming. If so, go ahead and finish the pattern! If not, you’ll probably want to choose a different approach.
In the end, you’re crocheting for yourself, so the only person who can tell you that what you’re making is wrong is you. If you like what you’re making, keep going! 🙂