Should I substitute sunlight with a grow lamp on cloudy days?

Hi fellow grower, Short answer long. Yes you can! Plants can experience light burn where the leaves are bleached on the tips where the light has been too intense. More often than not it comes with heat stress too. It will not hurt your plants to add more light and you're right to be cautious about intensity. Trial and error is the best way to learn. Set it up on 50% intensity and watch how your plants respond. Every plant is different, they all have their own characteristics and needs. I hope this helps, good luck with your grow...