diff --git a/src/fieldset.c b/src/fieldset.c
index 34c9fdf..eb5d27e 100644
--- a/src/fieldset.c
+++ b/src/fieldset.c
@@ -50,6 +50,26 @@ static inline void fs_add_word(fieldset_t *fs, const char *name, int type,
 	f->free_ = free_;
 }
 
+static void fs_modify_word(fieldset_t *fs, const char *name, int type,
+		int free_, size_t len, void *value)
+{
+	int i;
+	for (i=0; i<fs->len; i++) {
+		if (!strcmp(fs->fields[i].name, name)) {
+			if (fs->fields[i].free_) {
+				free((void*)fs->fields[i].value);
+				fs->fields[i].value = 0;
+			}
+			fs->fields[i].type = type;
+			fs->fields[i].free_ = free_;
+			fs->fields[i].len = len;
+			fs->fields[i].value = (uint64_t)value;
+			return;
+		}
+	}
+	fs_add_word(fs, name, type, free_, len, value);
+}
+
 void fs_add_null(fieldset_t *fs, const char *name)
 {
 	fs_add_word(fs, name, FS_NULL, 0, 0, NULL);
@@ -71,6 +91,28 @@ void fs_add_binary(fieldset_t *fs, const char *name, size_t len,
 	fs_add_word(fs, name, FS_BINARY, free_, len, value);
 }
 
+// Modify
+void fs_modify_null(fieldset_t *fs, const char *name)
+{
+	fs_modify_word(fs, name, FS_NULL, 0, 0, NULL);
+}
+
+void fs_modify_string(fieldset_t *fs, const char *name, char *value, int free_)
+{
+	fs_modify_word(fs, name, FS_STRING, free_, strlen(value), (void*) value);
+}
+
+void fs_modify_uint64(fieldset_t *fs, const char *name, uint64_t value)
+{
+	fs_modify_word(fs, name, FS_UINT64, 0, sizeof(uint64_t), (void*) value);
+}
+
+void fs_modify_binary(fieldset_t *fs, const char *name, size_t len,
+		void *value, int free_)
+{
+	fs_modify_word(fs, name, FS_BINARY, free_, len, value);
+}
+
 uint64_t fs_get_uint64_by_index(fieldset_t *fs, int index)
 {
 	return (uint64_t) fs->fields[index].value;
diff --git a/src/fieldset.h b/src/fieldset.h
index 9d49ba3..66de892 100644
--- a/src/fieldset.h
+++ b/src/fieldset.h
@@ -74,6 +74,8 @@ int fds_get_index_by_name(fielddefset_t *fds, char *name);
 
 void gen_fielddef_set(fielddefset_t *fds, fielddef_t fs[], int len);
 
+void fs_add_null(fieldset_t *fs, const char *name);
+
 void fs_add_uint64(fieldset_t *fs, const char *name, uint64_t value);
 
 void fs_add_string(fieldset_t *fs, const char *name, char *value, int free_);
@@ -81,9 +83,17 @@ void fs_add_string(fieldset_t *fs, const char *name, char *value, int free_);
 void fs_add_binary(fieldset_t *fs, const char *name, size_t len,
 		void *value, int free_);
 
-uint64_t fs_get_uint64_by_index(fieldset_t *fs, int index);
+// Modify
+void fs_modify_null(fieldset_t *fs, const char *name);
 
-void fs_add_null(fieldset_t *fs, const char *name);
+void fs_modify_uint64(fieldset_t *fs, const char *name, uint64_t value);
+
+void fs_modify_string(fieldset_t *fs, const char *name, char *value, int free_);
+
+void fs_modify_binary(fieldset_t *fs, const char *name, size_t len,
+		void *value, int free_);
+
+uint64_t fs_get_uint64_by_index(fieldset_t *fs, int index);
 
 void fs_free(fieldset_t *fs);