Method 1

1. File > External Data > Find Missing Files

It might be useful to enable "Find All" in options while browsing, if there are multiple libraries in the same folder or subfolders:

2. Choose the folder containing all library blend files.

Method 2

1. Outliner > Display Mode

2. Data API

3. Change the Library file path

The object that using that library will change.

Method 3

Scripting for batch operation

import bpy

for datablock in bpy.data.libraries:
    print(datablock.filepath)

    datablock.filepath = '..'

# Save the file and restart blender manually

Method 1

1. File > External Data > Find Missing Files

It might be useful to enable "Find All" in options while browsing, if there are multiple libraries in the same folder or subfolders:

2. Choose the folder containing all library blend files.

Method 2

1. Outliner > Display Mode

2. Data API

3. Change the Library file path

Save the file and restart blender,
The object that using that library will change.

Method 3

Scripting for batch operation

import bpy

for datablock in bpy.data.libraries:
    print(datablock.filepath)

    datablock.filepath = '..'

# Save the file and restart blender manually

Method 1

1. File > External Data > Find Missing Files

2. Choose the folder containing all library blend files.

Method 2

1. Outliner > Display Mode

2. Data API

3. Change the Library file path

Save File and restart blender,
The object that using that library will change.

Method 3

Scripting for batch operation

import bpy

for datablock in bpy.data.libraries:
    print(datablock.filepath)

    datablock.filepath = '..'

# Save the file and restart blender manually

Method 1

1. File > External Data > Find Missing Files

It might be useful to enable "Find All" in options while browsing, if there are multiple libraries in the same folder or subfolders:

2. Choose the folder containing all library blend files.

Method 2

1. Outliner > Display Mode

2. Data API

3. Change the Library file path

The object that using that library will change.

Method 3

Scripting for batch operation

import bpy

for datablock in bpy.data.libraries:
    print(datablock.filepath)

    datablock.filepath = '..'

# Save the file and restart blender manually