Hopefully you have at least a week to start pinning the cyp before your blend runs out and can make a smooth transition. If not you will likely feel a crash for 7-10 days while the short esters fall off and the cyp stabilizes, as Stairmaster said below. Nothing that you won't feel at the end of the cycle anyway.

Just out of curiosity, are you looking to extend your cycle longer than you originally planned to run it or did you just overlook the fact that you didn't have enough of the blend to run the full cycle in the beginning?

Its no problem , possible u feel a little "crash" when the short esters stop working but after 7-10 days all is fine again!

There is archival footage of those who Have tried the switch. Please watch before attempting.
https://youtu.be/n2ZpsbGr7s8

This is what I would do to keep my levels from fuctuating too much. Take how much of the sust you have devided by how many weeks you will run it and add however much test c to it to get the mg per week you need for your cycle. Example one and a half vials sust 250 mg/ml your running 500 mg per week for 12 weeks. So you have 3750 mg devide by 12 you have 300 mg available of sust per week add 200 mg cyp and boom

I usually kickstart with Prop. Shouldn’t be a problem.

This is why i don’t like them mixtures, someone has already decided for you what substances at what proportion you are going to be taking. If you want to increase one, all the others increase automatically, silly idea.
More likely you had longer eaters there too, therefore switching to Cyp or Enanthate will not be a problem. You need to calculate though how many mg/week was your mixture so you can adjust the mg of new substance

I would prefer to use testo-e or sustanon instead of cyp. But yes, you can switch. Don't forget: the longer your esters are, the more weight the ester has itself. So i would take some mg more, when switching to cyp ;)

It's fine test is test you will have a slight fluctuation but it will not be a big issue. I know a lot of people that start off their cycle with sust and switch it half way through. You will be fine mate

Its A ok

What esters were in the blend ? I'm curious as to why you started when you didn't have enough for your cycle ?