I don' t have any idea, why the name changed. Name changes seem to happen quite often, and Valborg Nilsdotters circumstances of surnames are quite complicated in itself. Moving from rural areas to Karlshamn seemed to have changed the surnames quite often (in Karlshamn the patronymic form of names very often was put aside for the (patronymic) surname of the father), first names normally just changed in their spellings. From Kjerstin to Kristina there seems to be no long way, as both may be shortened to Stina. At the first moving from Karlshamn may be the first discussion occurred, that she thought of being named Christina, so the clerk may be corrected the first name in the utflyttningsattest.
May be intersting f?r you are the following pages from Åryd, Hällaryd, Asarum and Karlshamn (following Valborgs life)
1781.18.74100 (Birth Valborg Nilsdotter, Åryd)
1756.6.103000 (Marriage of her parents Nils Peter Wästus and Juliana Lyberg, Åryd)
1781.18.85800 (Marriage Wallborg Nilsdotter and Åke Pehrsson Aborre, Åryd, 1788)
1756.8.4900 (Aborres death 1790, Hällaryd)
1756.8.5900 (Marriage Wallborg Nilsdotter and Ola Wassmann, Hällaryd, 1791)
1486.101.8800 (Hfl. Asarum 1794 - 1798)
1759.27.22100 (Hfl. 1820 - 1825, death Hans Peter Nordström and Nils Peter)
1759.27.44100 (Hfl. 1820 - 1825)
1759.5.101400 (Hfl. 1813 - 1819)
1759.4.86800 (Hfl. 1808 - 1813)
1759.3.62800 (Hfl 1803 - 1807)
1759.102.48500 (Marriage Hans Peter Jacobsson and Vallborg Nordström, Karlshamn, 1805)
1759.159.52100 (Wallborgs son Nils Peter, Karlshamn, 1801)
1759.160.94100 (Christinas oägta dotter Maria Axeliana, Karlshamn, 1825})