Hi Chriztian,

for a quick fix i would create a class, that goes to the back office services, loops through all the content, looking for the property - doing the fix and saving (or publishing) the changes.

if you make this class an UmbracoAuthorizedApiController, then you can just call it from a URL (once you are logged onto the back office)

e.g.

 using Umbraco.Core;
using Umbraco.Core.Models;
using Umbraco.Core.Services;
using Umbraco.Core.Logging;
using Umbraco.Web.Mvc;

public class PropertyFix : UmbracoAuthorizedController 
{

    public void FixContent()
    {
        var _contentService = ApplicationContext.Current.Services.ContentService;

        var rootContent = _contentService.GetRootContent();

        foreach(var item in rootContent)
        {
            FixContentItem(_contentService, item);
        }
    }

    public void FixContentItem(IContentService contentService, IContent item)
    {
        if (item.HasProperty("property") )
        {
            var p = item.GetValue<string>("property");

            // clean up property here.


            LogHelper.Info<PropertyFix>("Fixing Property on {0}", () => item.Name);
            item.SetValue("property", p);

            if (item.Published)
                contentService.Save(item);
            else
                contentService.SaveAndPublishWithStatus(item);
        }

        // do the children
        foreach(var child in item.Children())
        {
            FixContentItem(contentService, child);
        }
    }
}

you could then call FixContent from

/Umbraco/backoffice/Api/PropertyFix/FixContent

and you would see some logging in the umbraco log (app_data/logs)

just a note i haven't ran the code above! - test (and change ) it on something before you do your live site!!

K