Looking for a mod...

[narf poit chez BOOM]

Actually, if you go into settings.txt in the data folder, you can set wether mining decreases asteriod value in any mod or stock.

[Zereth]

Can you adjust how _much_ remote mining decreases value?

[Fyron]

Sadly, no.

In limited resource games, each planet has a maximum amount of resources that can be mined instead of a percent value. Every point of resource you mine decreases this value by one point. This applies to facilities as well (Mineral Miners, for example). Solar resource generation and the arbitrary point generation abilities added in 1.91 are exempt, however.