Hi, is there a method or is it possible to merge meshes to preserve its rigs and blendshapes?
Can you give me some StackOverflow examples?
Do you mean to merge meshes, where each has a separate rig - or merge meshes’ geometries and then apply a single rig to the result?
Yup. Exactly something like this
?Sorry, you were so fast 
Answer is: merge meshes, where each has a separate rig
While it doesn’t sound impossible - it’d likely wouldn’t be something easy to do.
Merging meshes is easy. But merging skeletons / rigs / armatures is less so.
Three maps armatures to skinIndex and skinWeight attributes on SkinnedMesh. To merge two or more skeletons together, you’d likely need to first put all bones of skeletons into a single Skeleton - then merge skinIndex and skinWeight attributes of both meshes, while offsetting the appended indices and weights by the amount of bones in each previous skeleton - then finally binding the merged skeleton to the merged mesh.
And while that all may actually work - you’ll quickly realise that you also need to rename all the bones in AnimationClips and decide to use Blender, or just put the multiple meshes and skeletons within a single group - and write a wrapper that’d help you control them together without merging 