A frame that the header is in need of splicing can be done very easily assuming you can get to both studs either side of the stud closest to the splice area. First one has to ascertain the reason for the slice, assuming this is done correctly and nothing untoward will be left after the splice, then the following might help -
Both the header and footer of a frame bind studs into a singularity, braced with dwangs (noggins) and occasionally diagonal braces, form a self standing structure. If a splice is inserted, say due to a cracked or rotted header, as long as the frame integrity is maintained, the frame will continue to perform it's function. Assuming any rotted wood is first dealt with, by proprietorial means, forming a bridle (cited for clarification sake only) under the splice to the two adjacent studs mentioned, supported at their ends with cripple studs should do the job, and is a practised way of doing it...bosshogg