: Lucene does not have any way to modify existing fields, so solr can't : do it either... (document boosts are stored as part of the field)
Actually, this question crossess over into a special case area. While you certianly can't "update" a Lucene doc, you can modify the fieldNorm of any [doc,field] pair using IndexReder.setNorm. So if you used TermFreqVectors (to see how many terms oare in the field), you could update the norm of a field using a new boost. changing just hte field boost or just the doc boost would be impossible (because no record is kept of what those independent values were) but changing just the total boost for some fields would be possible. -Hoss
