[Answer]-Modifying spatial widget formsets on Django admin

Normally you should use formfield_overrides property in TabularInline or StackableInline defenition.

For example:

from django.contrib import admin
from myapp.models import City, Shop

class ShopInline(admin.TabularInline):
    formfield_overrides = {
        models.PointField: {'widget': Textarea},
    }
    model = Shop

class CityAdmin(admin.ModelAdmin):
    inlines = [ShopInline,]

But If you want set widget for all inlines:

class DirectAdmin(admin.ModelAdmin):

def get_inline_instances(self, request, obj=None):

    overrides = {
        models.PointField: {'widget': Textarea},
    }
    inline_instances = super(DirectAdmin, self).get_inline_instances(request, obj=obj)
    for inline in inline_instances:
        inline.formfield_overrides = overrides
    return inline_instances

For better understanding please inspect get_inline_instance definition