Inserting blank frames

[Blues]

I record from digital TV broadcast, then I have to cut out the commercials and clean up the recording. For some weird reason sometimes the keyframe is from "wrong" fragment. It does not make sense, but it happens quite often. There is a keframe from the commercial and the very next frame is from content I want to keep. I have to leave the frame from commercial in or I lose some wanted content.
Audio editors allow inserting silence. If there is something I do not want I can silence it.
Would it be possible to replace this unwanted keyframe with a blank (of chosen color)? It would be much less annoying than a flash from ad.

[szlldm]

You can, but only when re-encode. However if you already re-encode, you can just cut those unwanted frame(s).

[Blues]

I cannot re-encode with Avidemux, cut only. This is the only way to preserve closed captions which are in MPEG-2 stream. Then Handbrake can read these captions and convert them into SSA while re-encoding.

[eumagga0x2a]

I cannot re-encode with Avidemux, cut only.

Please elaborate.

Oops, I missed the second sentence. Well, then you are out of options.