It is possible to change a rendition by overriding it. The following 0300-biggerThumbnails.json file changes the size of the doclib image from 100x100 to be 123x123 and introduces another rendition called biggerThumbnail that is 200x200.
{
"renditions": [
{
"renditionName": "doclib",
"targetMediaType": "image/png",
"options": [
{"name": "resizeWidth", "value": 123},
{"name": "resizeHeight", "value": 123},
{"name": "allowEnlargement", "value": false},
{"name": "maintainAspectRatio", "value": true},
{"name": "autoOrient", "value": true},
{"name": "thumbnail", "value": true}
]
},
{
"renditionName": "biggerThumbnail",
"targetMediaType": "image/png",
"options": [
{"name": "resizeWidth", "value": 200},
{"name": "resizeHeight", "value": 200},
{"name": "allowEnlargement", "value": false},
{"name": "maintainAspectRatio", "value": true},
{"name": "autoOrient", "value": true},
{"name": "thumbnail", "value": true}
]
}
]
}