I'm looking for a way to give a specific user the ability to make changes to Lead and Opportunity via the "Object Manager" screen without giving them access to full admin permissions.
I've seen this question, but the answer there suggests delegated administration, and the options for that only control editing custom objects so that doesn't seem to be what I require. Someone in the comments on that question suggested some permission in the normal permissions system but I can't find one. Note that even if delegated administration gave access to edit all standard objects by default, this is not what I want.
What is the solution for this? Is there one?
Customize application
permission gives the access to the users for managing fields, layouts etc. from the "Object Manager" screen for all/ most objects. (1) Do you want this user to view/ manage only the "Object Manager" screen for Lead & Oppty and nothing else in the setup pages? (2) Have you listed down what actions the user can perform on Lead & Oppty?without giving them access to full admin permissions.
>> (1) If there is no concern with user being able to view the admin pages and manage fields/ layouts on all objects, then simply clone the system admin or standard user profile & revoke all the access that would let him/ her edit the admin settings. You can do this simply via another profile or delegated admin. (2) On the other hand, if you have concerns, then there isn't an OOB functionality AFAIK. You could create a custom component, expose it to this user and use metadata API underneath for creation of fields in Leads and Oppty.