I know you said no string manipulation but i currently have the same problem and the only clean way I solved it for my self is to put it in a method:

public function getExampleAttributeStoragePath(){
        if($this->exampleAttribute){
            return str_replace("digitaloceanspaces","cdn.digitaloceanspaces",Storage::url($this->exampleAttribute));
        }else{
            return null;
        }
    }

But I also hope for a cleaner code, hope this helps as a quick fix for now

or you can also edit the url attribute in the filesystem config like this

'spaces' => [
            'driver' => 's3',
            'key' => env('DO_SPACES_KEY'),
            'secret' => env('DO_SPACES_SECRET'),
            'endpoint' => env('DO_SPACES_ENDPOINT'),
            'region' => env('DO_SPACES_REGION'),
            'bucket' => env('DO_SPACES_BUCKET'),
            'url' => str_replace(env('DO_SPACES_REGION'),env('DO_SPACES_BUCKET').'.'.env('DO_SPACES_REGION'),str_replace("digitaloceanspaces","cdn.digitaloceanspaces",env('DO_SPACES_ENDPOINT'))),
        ],

its a bit messy but does the job also this way its stored in the cache