You can't change the default material properties however you can create a custom material based off this material and change the yield strength. The S355 standard does imply a nominal minimum yield of 355Mpa however the material spec has some variation of the yield based on the thickness (see link below). You should contact a local supplier for the material and verify the properties for the thickness you are using and then create a custom material in Solidworks.
Yield strength is really only used for fos plot, so even if it isn't correct, it won't invalidate your results. Only E and v are important in static. K and p if you have thermal and gravity/centrifugal loads.