How to find text and replace next line.?

Have multiple files with the same format and certain text is the same. Have specific text to search for and then need to replace the next line. Can search on the text DEVICE and multiple lines will be found. The line after each DEVICE line has {. Want to replace the line { with {-someadditiontext. The problem is that there are other lines that have { and do not want to change them, only the ones that have the word DEVICE in the previous line. How could this be done in a script?

Example of file to be modified:

DATALIST "Test"
GROUP "Test Group"
DYNAMIC 1 3
DEFAULTS
{
        FILESYSTEM
        {
        }  
        RAWDISK
        {
        }
}
DEVICE "Test Drive"
{
}
DEVICE "Test Drive"
{
}

With your sample input, the command:

sed '/DEVICE/{
	N
	s/{/{-someadditiontext/
}' file

produces the output:

DATALIST "Test"
GROUP "Test Group"
DYNAMIC 1 3
DEFAULTS
{
        FILESYSTEM
        {
        }  
        RAWDISK
        {
        }
}
DEVICE "Test Drive"
{-someadditiontext
}
DEVICE "Test Drive"
{-someadditiontext
}

Is that what you wanted?

That is exactly what I needed, thank you!