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This mod/data pack simply changes the mobExplosionDropDecay gamerule to false to make creeper explosions drop all the destroyed blocks, so you can fill it back in.
go to your saves folder located here on Windows:
C:\Users(your name)\AppData\Roaming\.minecraft\saves
put the zipped file in the data packs folder, and either restart your world or execute /reload

Makes Creeper (and ghast) explosions drop all the affected blocks!