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I have never had an issue changing the URL for a place page, either old Places style or new G+ social.

URL was never part of the old NAP based id system, and it is quite common for a business to change/update the URL of there business. I would feel safe in making that change on your page.

In the past, Google Local listings where governed by what is called the NAP - Name, Address, Phone. Changing any of these three elements 'could' cause the listing to break away from the reviews. This was also complicated by the fact that data for your listing was stored in multiple databases for Places, MapMaker and Google+ and the data would be syncing from one DB to the other all the time, often causing edits to revert to an older version.

BUT, as Google now moves more towards the Google+ Social model they have also moved to a single/central DB for local listings. With this new model, if your local listing is claimed and verified AND upgraded to a Google+ social listing, things become much more stable, and seem to no longer use the fragile NAP based system. I have been able to edit Name, Address and Phone, move the marker to a new location and have all my reviews safely move with me.

If you attempt to edit those and your listing is just a regular Place listing and not Google+ social (has the posts tab) then you are almost certain to loose your reviews in the process.

In the past, Google Local listings where governed by what is called the NAP - Name, Address, Phone. Changing any of these three elements 'could' cause the listing to break away from the reviews. This was also complicated by the fact that data for your listing was stored in multiple databases for Places, MapMaker and Google+ and the data would be syncing from one DB to the other all the time, often causing edits to revert to an older version.

BUT, as Google now moves more towards the Google+ Social model they have also moved to a single/central DB for local listings. With this new model, if your local listing is claimed and verified AND upgraded to a Google+ social listing, things become much more stable, and seem to no longer use the fragile NAP based system. I have been able to edit Name, Address and Phone, move the marker to a new location and have all my reviews safely move with me.

If you attempt to edit those and your listing is just a regular Place listing and not Google+ social (has the posts tab) then you are almost certain to loose your reviews in the process.