Sadly assets are currently not part of the Migration CLI.
Do you derive the value for the asset from an entry? Then you might be able to use the contentful-management SDK as a workaround within the function.
The migration & transformEntryForLocale methods accepts returning a Promise, so you could manually set the new value for the asset via the SDK and then return the value for the entry.
// previously initialize the client with space & accesstoken (env/argv - consider yargs)
async function transformEntryForLocale (fields, locale) {
const asset = await space.getAsset(fields.myAsset.sys.id)
asset.fields.title[locale] = 'New Title'
await asset.save()
return fields[locale]
}
Would something like this be able to solve your usecase?