Here's the CSS trick.
Give your filemanager widget a css class, e.g. myuploader
Then add the following styling trick to your css
.myuploader .mx-fileinput-upload-button {
font-size: 0px;
}
.myuploader .mx-fileinput-upload-button:before {
font-size: 12px; /* asuming this is your fontsize; change, if needed */
content: "custom button text";
}
Regarding cropping images: See https://appstore.home.mendix.com/link/app/254/Mendix/Image-Crop.
Regarding the specific button text: - Maybe this specific text can be achieved with some CSS/JS tricks. - Otherwise you will need a widget which will open the select file dialog via JS I think. Although I would not go there unless absolutely necessary.