I suggest this solution

1. Add new values on the country & district picklist for example

--CurrentUserCountry--

--CurrentUserDisctrict--

2. Set those values as the default values for country & district picklists on the Opp

3. Create a process builder that fires on Opportunity Create

4. When the country & district are still set to the default values

update them through the process builder to the user's country & district

If the values are different from the default values that means the user changed them, so you don't need to override the values

I suggest this solution

1. Add new values on the country & district picklist for example

--CurrentUserCountry--

--CurrentUserDisctrict--

2. Set those values as the default values for country & district picklists on the Opp

3. Create a process builder that fires on Opportunity Create

4. When the country & district are still set to the default values, update them through the process builder to the user's country & district

If the values are different from the default values that means the user changed them, so you don't need to override the values

I suggest this solution

Add new values on the country & district picklist for example

--CurrentUserCountry--

--CurrentUserDisctrict--

Set those values as the default values for country & district picklists on the Opp

Create a process builder that fires on Opportunity Create

When the country & district are still set to the default values

update them through de process builder to the user's country & district

If the values are different from the default values that means the user changed them, so you don't need to override the values

I suggest this solution

1. Add new values on the country & district picklist for example

--CurrentUserCountry--

--CurrentUserDisctrict--

2. Set those values as the default values for country & district picklists on the Opp

3. Create a process builder that fires on Opportunity Create

4. When the country & district are still set to the default values

update them through the process builder to the user's country & district

If the values are different from the default values that means the user changed them, so you don't need to override the values