The box will tell you to tint the regrowth for the full time and to pull the colour through to the end for the last 10 minutes. Well this will indeed balance the shade, but it will also damage your ends further.
Every time you touch your hair with colour that lightens your natural base tone, you will get damage.. add that up, time and time again, and you will have a horror story.
I highly recommend you balance the ends with a totally non damaging pigment. The shades available may not match exactly, but you should be able to find something quite close. The condition of your hair will be left amazing and soft, with no damage at all. Do be aware this stuff stains like crazy so make sure to wear gloves. You can use Soft Colour as often as you like, so in between tinting your regrowth, you can have totally fresh hair.
Goldwell Soft Color Foam Colorant reviews - Makeupalley