SYMBOLS REPLACE

Can anyone advise me how to replace all the symbols on the page with another symbol. I explain: I have 50 labels on page 1 marked weight 750 g. All labels are symbols. I copy the first page and thus create a second page with the same tags. I want to change the weight to 400. I edit one symbol changing 700 to 400 but the labels on the first page change too.

My idea is on the second page to restore one symbol next to objects, change 750 to 400 and then group the objects for one label and create a new symbol. Then I need a way for the new symbol to replace the old one on the second page. Now I do this manually and it's very annoying.

Greetings!