This is not currently possible using the JSON specification for plugin parameters. I will add your request to our backlog.
Note that if your need is to enforce bounds on DOUBLE or INT parameters, you can do it using minI/maxI (for INT) and minD/maxD (for DOUBLE). You can check an example here.
If your need is specific to date, as your screenshot indicates, I would advise using directly a DATE parameter.
Hope it helps,
How can we have a vertical separator as the list of variables on the datasets page is getting long and therefore, we are bound to scroll to fill the variable values?
We were hoping to utilize the space on the left of the screen (cross marked).
The space on the left of the custom dataset screen is intended for the dataset preview. Therefore it is not possible to fill it with custom parameters.