Took me about two years of trying every single shot. I got to maybe nine out of ten. After that I used position more to stall than to make balls. It was brutal. Before jump cues, there were a few jump rods around, but by and large you only needed to put a small slice of ball blocking a shot for it to be a safety.
Everything was accidental. Accidental safeties, accidentally hooking myself to keep the other player in the game. The other player could see if the shot had rolled a tiny bit further or a tiny bit less they would have had an open table. Which reminds me, perfect speed control was needed for a lot of shots. Perfect speed control is going to be tougher to get now than it was then. There was the slow directional cloth still around a bit when I started, the fast cloth of the eighties which would be better called medium speed, and the fast cloth of today which is faster than greased owl crap.
Hate to bring the pursuit into play but artistic pool used to be played in two stages. The first stage was shots from the book of artistic pool. The second stage was select your own shots. You would get two tries at a shot you had practiced a lot, the other player got two tries at that same shot and you alternated turns leading I believe, make or miss. Sounds a lot like what you have in mind. It would be artistic pool lite.
Lola, good luck on spot shape. You should be able to put an aspirin sized piece of paper on the table and shade it the vast majority of the time. Rob a paper hole punch for your targets. The cue ball should stop with at least an edge of the cue ball over the paper. Just for convenience you might start with a dime but after awhile the dime interferes with the shot too often. I think you might get to seven out of ten which means you will have to think more about angles than Willie Mosconi did in his day. He would come across the shooting lanes and go ten for ten some sessions when he was a young man. He was the one that caused me gray and thinning hair when I was young. I thought I was playing shape when I could hit the next ball. I was a shotmaker as described by some in this thread. Willie made me rethink what was possible! Two people made me rethink what was possible about twenty years apart, Willie and Efren. I wouldn't say either was better than the other, they were different. There have been a lot of other players out there, some serious beasts, but none that made me say, damn I didn't know that was possible! Not talking about trick shot artists, the best of those aren't shooting pool but have brought the pursuit of their craft well past what I considered possible. I think it was Sang Lee that didn't impress my young practice partner. "I see those shots all the time," Yeah, but others are still maybe 50% on them and Sang Lee invented those shots decades ago! I wish you the best. You are on a lonely path chasing spot shape.
Hu