Working with limitations and alterations teaches me a lot. Here are some that have helped me shake habits of overdoing, among other classes of vocal faults.
Exhale most of the air from your body before singing. Singing after exhaling feels very different but can be surprisingly good for efficiency and and clarity of sound. Overbreathing is a classic fault of many singers. Less might be more!
Slump in a chair very relaxed, then sing. Which parts of your body are contributing to your sound and which are turned off in this position? Compare to standing which feels different. Does it sound as different as it feels? In what ways?
Sing a phrase with a wrong vowel on every note. For example: “the water is wide” becomes “though widow as wade”. Does the phrase get easier or harder? Why?
While sitting with your back supported by a chair, or after a big exhale with no inhale, or both(!), try singing a 8-5-3-1-3-5-8 pattern in various parts of your range. Repeat standing tall. Which way is easier?
Sing the pitches from above “bottom up”, 1-3-5-8-5-3-1. How do the lowest and highest notes feel and sound different from before? How about starting and ending in the middle, e.g., 5-3-1-3-5-8-5?
Sometimes, surprisingly good singing pops out when we get out of perfection mode and mess things up a little bit.