diff --git a/hw/nvram/fw_cfg.c b/hw/nvram/fw_cfg.c
index 7dc3ac378e..aef1727250 100644
--- a/hw/nvram/fw_cfg.c
+++ b/hw/nvram/fw_cfg.c
@@ -690,6 +690,15 @@ void fw_cfg_add_string(FWCfgState *s, uint16_t key, const char *value)
     fw_cfg_add_bytes(s, key, g_memdup(value, sz), sz);
 }
 
+void fw_cfg_modify_string(FWCfgState *s, uint16_t key, const char *value)
+{
+    size_t sz = strlen(value) + 1;
+    char *old;
+
+    old = fw_cfg_modify_bytes_read(s, key, g_memdup(value, sz), sz);
+    g_free(old);
+}
+
 void fw_cfg_add_i16(FWCfgState *s, uint16_t key, uint16_t value)
 {
     uint16_t *copy;
@@ -720,6 +729,16 @@ void fw_cfg_add_i32(FWCfgState *s, uint16_t key, uint32_t value)
     fw_cfg_add_bytes(s, key, copy, sizeof(value));
 }
 
+void fw_cfg_modify_i32(FWCfgState *s, uint16_t key, uint32_t value)
+{
+    uint32_t *copy, *old;
+
+    copy = g_malloc(sizeof(value));
+    *copy = cpu_to_le32(value);
+    old = fw_cfg_modify_bytes_read(s, key, copy, sizeof(value));
+    g_free(old);
+}
+
 void fw_cfg_add_i64(FWCfgState *s, uint16_t key, uint64_t value)
 {
     uint64_t *copy;
@@ -730,6 +749,16 @@ void fw_cfg_add_i64(FWCfgState *s, uint16_t key, uint64_t value)
     fw_cfg_add_bytes(s, key, copy, sizeof(value));
 }
 
+void fw_cfg_modify_i64(FWCfgState *s, uint16_t key, uint64_t value)
+{
+    uint64_t *copy, *old;
+
+    copy = g_malloc(sizeof(value));
+    *copy = cpu_to_le64(value);
+    old = fw_cfg_modify_bytes_read(s, key, copy, sizeof(value));
+    g_free(old);
+}
+
 void fw_cfg_set_order_override(FWCfgState *s, int order)
 {
     assert(s->fw_cfg_order_override == 0);
diff --git a/include/hw/nvram/fw_cfg.h b/include/hw/nvram/fw_cfg.h
index 80e435d303..b5291eefad 100644
--- a/include/hw/nvram/fw_cfg.h
+++ b/include/hw/nvram/fw_cfg.h
@@ -98,6 +98,20 @@ void fw_cfg_add_bytes(FWCfgState *s, uint16_t key, void *data, size_t len);
  */
 void fw_cfg_add_string(FWCfgState *s, uint16_t key, const char *value);
 
+/**
+ * fw_cfg_modify_string:
+ * @s: fw_cfg device being modified
+ * @key: selector key value for new fw_cfg item
+ * @value: NUL-terminated ascii string
+ *
+ * Replace the fw_cfg item available by selecting the given key. The new
+ * data will consist of a dynamically allocated copy of the provided string,
+ * including its NUL terminator. The data being replaced, assumed to have
+ * been dynamically allocated during an earlier call to either
+ * fw_cfg_add_string() or fw_cfg_modify_string(), is freed before returning.
+ */
+void fw_cfg_modify_string(FWCfgState *s, uint16_t key, const char *value);
+
 /**
  * fw_cfg_add_i16:
  * @s: fw_cfg device being modified
@@ -136,6 +150,20 @@ void fw_cfg_modify_i16(FWCfgState *s, uint16_t key, uint16_t value);
  */
 void fw_cfg_add_i32(FWCfgState *s, uint16_t key, uint32_t value);
 
+/**
+ * fw_cfg_modify_i32:
+ * @s: fw_cfg device being modified
+ * @key: selector key value for new fw_cfg item
+ * @value: 32-bit integer
+ *
+ * Replace the fw_cfg item available by selecting the given key. The new
+ * data will consist of a dynamically allocated copy of the given 32-bit
+ * value, converted to little-endian representation. The data being replaced,
+ * assumed to have been dynamically allocated during an earlier call to
+ * either fw_cfg_add_i32() or fw_cfg_modify_i32(), is freed before returning.
+ */
+void fw_cfg_modify_i32(FWCfgState *s, uint16_t key, uint32_t value);
+
 /**
  * fw_cfg_add_i64:
  * @s: fw_cfg device being modified
@@ -148,6 +176,20 @@ void fw_cfg_add_i32(FWCfgState *s, uint16_t key, uint32_t value);
  */
 void fw_cfg_add_i64(FWCfgState *s, uint16_t key, uint64_t value);
 
+/**
+ * fw_cfg_modify_i64:
+ * @s: fw_cfg device being modified
+ * @key: selector key value for new fw_cfg item
+ * @value: 64-bit integer
+ *
+ * Replace the fw_cfg item available by selecting the given key. The new
+ * data will consist of a dynamically allocated copy of the given 64-bit
+ * value, converted to little-endian representation. The data being replaced,
+ * assumed to have been dynamically allocated during an earlier call to
+ * either fw_cfg_add_i64() or fw_cfg_modify_i64(), is freed before returning.
+ */
+void fw_cfg_modify_i64(FWCfgState *s, uint16_t key, uint64_t value);
+
 /**
  * fw_cfg_add_file:
  * @s: fw_cfg device being modified