GIMP Script-fu

sg-anim-settings
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Command:
Settings...
Menu:
"<Image>/Filters/Animation/Settings..."
PDB Name:
script-fu-sg-anim-settings
Download:
sg-anim-settings.scm (after the page appears, click on the "Download" command)
License:
GPLv2+

Description:

The "Animation->Settings" command permits changing of the delay and disposition of the layers in an animated GIF. The delay can be set to any value up 10000 milli-seconds (10 seconds). or it can be cleared.

The Mode parameter specifies the frame disposition of the layer and is typically either "combine" or "replace".

Clearing a setting is not generally necessary, but it can be useful for making cosmetic changes to the layername.

The script only affects the visible layers so hide layers that you do not wish to be changed. N.B., after using the "Filters->Animation->Playback" player, you are returned to a state where only a single layer is visible (this is probably not what you'd want if you are planning on using this script afterward).