If a polynomial has already been created and maybe even the participants' shares were computed, there is still the possibility of modifying this part of the scheme.
Based on the secret S, threshold t and number of participants n you can call a dialog by clicking the button Edit polynomial parameters of the setup dialog at any point of time.
At the top of the dialog all the unchangeable parameters are displayed. Below are two separate input text boxes. One shows your current prime p, the other shows the coefficients of the polynomial, separated by commas.
There are two options of modifying parameters:
On the one hand, a new prime and according coefficients can be created randomly by choosing the button Generate polynomial.
On the other hand, you can manually modify parameters. Modifications are accepted by left-clicking the OK button. Of course, manual changes are checked before they are adopted. If any of the values do not match Shamir's criteria, CrypTool will alert you.