Welcome to Onyx! Yes, you can obtain standardized coefficients; right-click on the path with the parameter you are interested in and choose ‘Customize Path’ -> ‘Show Standardized Estimates’. This will give you the standardized estimate on regression paths and the correlation on covariance paths.
Onyx can give you the modificiation index for any nesting (in particular, for setting a single parameter to zero, which I guess is what you are looking for first); for this, you can copy your model (best with ‘Edit’ -> ‘Clone Model’) and delete the target path there. Then, connect the two models by a path (just right-click on any empty space in one model, drag to the other model, and release the right button there). On the connecting path, there is a dot which will give you the LR (which, for a single parameter, is the MI). I know it would be convenient to get one big table with all MIs for all parameters, it’s on the todo-list, but will take some time (it’s a looong list :).
Cheers & Happy Eastern,