If you are looking to work out your muscles, then it’s necessary to change your routines to merely prevent your body from getting used to the motions you are putting it through and gain something from the movements you are doing.
If you are only stretching, you can do the same stretches every day. It’s more beneficial, and you will notice your progress more easily than if you switch up your routines.
So I think its good but only "NECESSARY" when needed and if there is a specific issue or reason. You can do the same stretch for months and it can and should start to feel different because now you are more flexible and comfortable. But by all means if it is too painful stretch only to you capacity. Also, adding in stretches can be considered as switching it up, which is completely cool, yet again noy Neccessary! As long as you stretch the entire body and especially the areas you feel is most needed, you should be fine! 😊Thank you for your question! I hope this helps.