You can change your product price for both new and existing customers.
How to change prices for new customers
The first thing you'll want to do is duplicate your product
Once you are on the Subscription Products list view, if you hover your mouse over the product you want duplicated you will see a duplicate button appear on the right hand side of that product. Click duplicate and a exact copy of your product will be created.
Once your new product is created go to the details page of your old product.
Navigate to the Visibility toggle and turn it off:
Your store should now only show the product with updated pricing for all new subscribers.
Should you want to update your existing customers to the new product with the updated pricing, you can follow this guide: How to change the product your customer is subscribed to.
Changing your Product weight
If you want to change the weight of the product and you have subscribers you can do that! Simply go to your product and change the weight. From there you can decide if you want that new weight to be applied to all existing subscriptions or just new subscribers.
Changing this product's weight may impact the shipping cost for your Active Subscribers. Any reactivating subscribers will also reflect the product weight.
Be sure to notify your existing subscribers about this potential shipping cost change to avoid complaints and chargebacks.