You say that you're not at a point where your brain will accept statements that you make. I can understand this, but...
Your brain will not accept something that it rejects because it seems too much of a leap. What about creating something that is completely universally acceptable? The statements in the therapy and the ones you put here as examples, that's exactly why they are like they are - they're not trying to be super duper over the top confident. People can be over the top confident, and good for them. But for us, now, we want our brains to accept anything that is just reasonable.
I think customizing the therapy and making it into your own words is ALWAYS a good idea. I don't know that this is right or wrong, I'm just saying my opinion. There is no wrong. So... I think you could make therapy statements that reflect your situations, your reality, your concerns for the day, and you make them in a way which is acceptable for you because you can agree that the same truth is acceptable for all people. This might be a way for you to come up with more statements.
I think you bring up a good point here - the place we start from is at a point where we cannot jump to being overly optimistic. This I see as one reason other professionals don't really understand how to help us get better. This is one problem why certain books don't help. They think you can jump right to the good stuff. They don't realize the time it takes to go from negative, to slightly negative, to slightly neutral, to neutral, to slightly positive, to... They think we start from neutral and just try to jump to positive. This is kinda why no one understands us with these feelings. The time it takes for us to accept rational thoughts.
Use the therapy statements if that is what you can accept for now. There is no problem with these! Try making your own for the situations you encounter, only if you like. Anyway, you're just trying, right? You can't fail. There's no failing or judgement here.
I strayed a bit from your intention, but I'm glad to see you are doing the therapy! Hang in there.